[T-Mobile Samsung Galaxy S II SGH-T989] Splaktar:
Here are some logcats from turning on and off USB storage:

E/VoldConnector( 597): NDC Command {8 volume mount /storage/sdcard1} took too long (13400ms)
E/VoldConnector( 597): NDC Command {9 volume mount /storage/sdcard0} took too long (11494ms)
...
E/VoldConnector( 597): NDC Command {43 volume unmount /storage/sdcard0 force} took too long (3277ms)
E/VoldConnector( 597): NDC Command {46 volume unmount /storage/sdcard1 force} took too long (1091ms)

Nothing too ground breaking, but it is quite easy to hang the device and require hard booting it.

Update here are some more, not sure that they are helpful at all though:

E/VoldConnector( 597): NDC Command {51 volume mount /storage/sdcard0} took too long (15060ms)
E/VoldConnector( 597): NDC Command {52 volume shared /storage/sdcard0 ums} took too long (15049ms)
E/VoldConnector( 597): NDC Command {56 volume mount /storage/sdcard1} took too long (4299ms)
E/VoldConnector( 597): NDC Command {57 volume shared /storage/sdcard0 ums} took too long (4246ms)
E/VoldConnector( 597): NDC Command {58 asec fspath net.androgames.level-1} took too long (4026ms)
E/Vold ( 226): ASEC kr.aboy.tools-1 already mounted
E/SecondaryTablController( 229): ip route del failed: /system/bin/ip route del 21.xx.xx.233/32 via 0.0.0.0 dev rmnet_sdio0 table 60
E/SecondaryTablController( 229): ip route del failed: /system/bin/ip route del 0.0.0.0/0 via 21.40.86.233 dev rmnet_sdio0 table 60
E/Nova.Workspace( 1020): The Hotseat screen must be >= 0 and < 1 (was 1); skipping child
E/Nova.Workspace( 1020): The Hotseat screen must be >= 0 and < 1 (was 2); skipping child

Here are some from after the sdcards were finally mounted, but the media scanner is still trying to run:

E/MediaScannerJNI( 2228): An exception was thrown by callback 'scanFile'.
E/MediaScannerJNI( 2228): java.lang.NullPointerException
E/MediaScannerJNI( 2228): at android.media.MediaScanner.makeEntryFor(MediaScanner.java:1489)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.beginFile(MediaScanner.java:472)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.doScanFile(MediaScanner.java:526)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.scanFile(MediaScanner.java:518)
E/MediaScannerJNI( 2228): at android.media.MediaScanner.processDirectory(Native Method)
E/MediaScannerJNI( 2228): at android.media.MediaScanner.scanDirectories(MediaScanner.java:1302)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.scan(MediaScannerService.java:105)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.access$300(MediaScannerService.java:49)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService$ServiceHandler.handleMessage(MediaScannerService.java:271)
E/MediaScannerJNI( 2228): at android.os.Handler.dispatchMessage(Handler.java:99)
E/MediaScannerJNI( 2228): at android.os.Looper.loop(Looper.java:137)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.run(MediaScannerService.java:186)
E/MediaScannerJNI( 2228): at java.lang.Thread.run(Thread.java:856)
E/MediaScannerJNI( 2228): An error occurred while scanning directory '/storage/sdcard0'.
E/MediaScannerJNI( 2228): An exception was thrown by callback 'scanFile'.
E/MediaScannerJNI( 2228): java.lang.NullPointerException
E/MediaScannerJNI( 2228): at android.media.MediaScanner.makeEntryFor(MediaScanner.java:1489)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.beginFile(MediaScanner.java:472)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.doScanFile(MediaScanner.java:526)
E/MediaScannerJNI( 2228): at android.media.MediaScanner$MyMediaScannerClient.scanFile(MediaScanner.java:518)
E/MediaScannerJNI( 2228): at android.media.MediaScanner.processDirectory(Native Method)
E/MediaScannerJNI( 2228): at android.media.MediaScanner.scanDirectories(MediaScanner.java:1302)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.scan(MediaScannerService.java:105)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.access$300(MediaScannerService.java:49)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService$ServiceHandler.handleMessage(MediaScannerService.java:271)
E/MediaScannerJNI( 2228): at android.os.Handler.dispatchMessage(Handler.java:99)
E/MediaScannerJNI( 2228): at android.os.Looper.loop(Looper.java:137)
E/MediaScannerJNI( 2228): at com.android.providers.media.MediaScannerService.run(MediaScannerService.java:186)
E/MediaScannerJNI( 2228): at java.lang.Thread.run(Thread.java:856)
E/MediaScannerJNI( 2228): An error occurred while scanning directory '/storage/sdcard1'.

And some more while trying to unmount USB storage:

E/MediaScannerService( 2228): Exception in handleMessage
E/MediaScannerService( 2228): android.os.DeadObjectException
E/MediaScannerService( 2228): at android.os.BinderProxy.transact(Native Method)
E/MediaScannerService( 2228): at android.media.IMediaScannerListener$Stub$Proxy.scanCompleted(IMediaScannerListener.java:100)
E/MediaScannerService( 2228): at com.android.providers.media.MediaScannerService$ServiceHandler.handleMessage(MediaScannerService.java:251)
E/MediaScannerService( 2228): at android.os.Handler.dispatchMessage(Handler.java:99)
E/MediaScannerService( 2228): at android.os.Looper.loop(Looper.java:137)
E/MediaScannerService( 2228): at com.android.providers.media.MediaScannerService.run(MediaScannerService.java:186)
E/MediaScannerService( 2228): at java.lang.Thread.run(Thread.java:856)
E/MediaScannerService( 2228): Exception in handleMessage
E/MediaScannerService( 2228): android.os.DeadObjectException
E/MediaScannerService( 2228): at android.os.BinderProxy.transact(Native Method)
E/MediaScannerService( 2228): at android.media.IMediaScannerListener$Stub$Proxy.scanCompleted(IMediaScannerListener.java:100)
E/MediaScannerService( 2228): at com.android.providers.media.MediaScannerService$ServiceHandler.handleMessage(MediaScannerService.java:251)
E/MediaScannerService( 2228): at android.os.Handler.dispatchMessage(Handler.java:99)
E/MediaScannerService( 2228): at android.os.Looper.loop(Looper.java:137)
E/MediaScannerService( 2228): at com.android.providers.media.MediaScannerService.run(MediaScannerService.java:186)
E/MediaScannerService( 2228): at java.lang.Thread.run(Thread.java:856)

I'm also seeing this at times (Youtube ANR), this happens when mounting USB Storage:

E/ConnectivityService( 597): startUsingNetworkFeature took too long: 34040ms
E/ActivityManager( 597): ANR in com.google.android.youtube
E/ActivityManager( 597): Reason: Executing service com.google.android.youtube/.core.transfer.DownloadService

Not sure what these are all about, but I've seen them a couple times now after unmounting USB storage:

E/MediaPlayer( 801): error (1, -2147483648)
E/AudioHardwareMSM8660( 235): write(): dec_id = 1 cur_rx = 2
E/AudioHardwareMSM8660( 235): cur_rx for pcm playback = 2
E/ ( 235): [ACDB RTC]->rtc init done!->result [0]
E/ ( 235): actp_diag_init: call diag init function with 40E80951
E/ ( 235): [ACDB ACPH]->actp diag init done!
E/ACDB-LOADER( 235): Error reading MBHC general config returned = fffffff3
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/ACDB-LOADER( 235): Error: ACDB ANC returned = -8
E/AudioHardwareMSM8660( 235): value of device and enable is 2 1 ALSA dev id:2
E/MP-Decision( 1457): DOWN Ld:14 Ns:1.100000 Ts:190 rq:0.500000 seq:194.000000
E/AudioHardwareMSM8660( 235): value of device and enable is 2 0 ALSA dev id:2
E/AudioHardwareMSM8660( 235): value of device and enable is 3 0 ALSA dev id:3