[Galaxy S I9000 Q&A, Help & Troubleshooting] Stefanauss:
You're probably asking the wrong person.

JM7 and JM8 has no perceivable difference or features... except speed, for me. JM7 was the worst fw i tried, by far, sluggy as hell. I used a super-clean flash for both, updating the same way for both, but the results are incomparable

If you are unsatisfied with JM7 lag-wise (we know it's laggy by definition, but i mean, if you're really pissed off with what you have) maybe it's worth a try.

EDIT: Forget it, i was curious too and i did a comparison about the filesystem.

Here is the files that change between JM7 and JM8, and so they have probably got the developers' attention.

sending incremental file list
build.prop
app/
app/AccountAndSyncSettings.odex
app/ApplicationsProvider.odex
app/AxT9IME.apk
app/AxT9IME.odex
app/BadgeProvider.odex
app/Bluetooth.odex
app/BluetoothOPP.odex
app/BluetoothServices.odex
app/BluetoothTestMode.odex
app/Browser.odex
app/BuddiesNow.odex
app/CSC.odex
app/CallSetting.odex
app/Camera.odex
app/CameraFirmware.odex
app/CertInstaller.odex
app/ClockPackage.odex
app/Contacts.odex
app/ContactsProvider.odex
app/DataCreate.odex
app/Days.odex
app/DialerTabActivity.odex
app/Divx.odex
app/Dlna.odex
app/DownloadProvider.odex
app/DrmProvider.odex
app/DrmUA.odex
app/DualClock.odex
app/Email.odex
app/FMRadio.odex
app/FactoryTest.odex
app/FlashPlugin.odex
app/FlashSVGPlayer.odex
app/Gallery3D.odex
app/GlobalSearch.odex
app/GoogleSearch.odex
app/HTMLViewer.odex
app/IcsService.odex
app/InfoAlarm.odex
app/InputEventApp.odex
app/JobManager.odex
app/LbsTestMode.odex
app/LiveWallpapers.odex
app/LiveWallpapersPicker.odex
app/LogsProvider.odex
app/MagicSmokeWallpapers.odex
app/MediaProvider.odex
app/Memo.odex
app/MiniDiary.odex
app/Mms.odex
app/MobileAP.odex
app/MobileTrackerEngineTwo.odex
app/MobileTrackerUI.odex
app/MtpApplication.odex
app/MusicPlayer.odex
app/MyFiles.odex
app/OtaProvisioningService.odex
app/PackageInstaller.odex
app/Personalization.odex
app/Phone.odex
app/PhoneCrashNotifier.odex
app/PhoneErrService.odex
app/Phone_Util.odex
app/PicoTts.odex
app/Preconfig.apk
app/Preconfig.odex
app/RilFactoryApp.odex
app/SamsungWidget_CalendarClock.odex
app/SamsungWidget_FeedAndUpdate.odex
app/SamsungWidget_ProgramMonitor.odex
app/SamsungWidget_StockClock.odex
app/SamsungWidget_WeatherClock.odex
app/SecDownloadProvider.odex
app/Settings.odex
app/SettingsProvider.odex
app/SisoDrmProvider.odex
app/SnsAccount.odex
app/SnsProvider.odex
app/SoundPlayer.odex
app/Stk.odex
app/TATLiveWallpapersAurora.odex
app/TATLiveWallpapersBlueSea.odex
app/TATLiveWallpapersDandelion.odex
app/TATLiveWallpapersOceanWave.odex
app/TelephonyProvider.odex
app/TouchWiz30Launcher.odex
app/TouchWizCalculator.odex
app/TouchWizCalendar.odex
app/TouchWizCalendarProvider.odex
app/TtsService.odex
app/TwWallpaperChooser.odex
app/UNAService.odex
app/UnifiedInbox.odex
app/UserDictionaryProvider.odex
app/VideoPlayer.odex
app/VisualizationWallpapers.odex
app/VoiceDialer.odex
app/VoiceRecorder.odex
app/VpnServices.odex
app/WlanTest.odex
app/WriteandGo.odex
app/lcdtest.odex
app/serviceModeApp.odex
app/shutdown.odex
app/signin.odex
app/syncmldm.odex
app/syncmlds.odex
app/wipereceiver.odex
app/wssomacp.odex
app/wssyncmlnps.odex
bin/
bin/cat
bin/chmod
bin/chown
bin/cmp
bin/date
bin/dd
bin/debuggerd
bin/df
bin/dmesg
bin/dumpcrash
bin/dumpmesg
bin/getevent
bin/getprop
bin/hd
bin/id
bin/ifconfig
bin/iftop
bin/insmod
bin/ioctl
bin/kill
bin/ln
bin/log
bin/ls
bin/lsmod
bin/mkdir
bin/mount
bin/mv
bin/netstat
bin/newfs_msdos
bin/notify
bin/printenv
bin/ps
bin/reboot
bin/renice
bin/rm
bin/rmdir
bin/rmmod
bin/route
bin/schedtop
bin/sendevent
bin/setconsole
bin/setprop
bin/sleep
bin/smd
bin/start
bin/stop
bin/sync
bin/top
bin/umount
bin/vmstat
bin/watchprops
bin/wipe
bin/gpsd/
cameradata/
etc/
etc/bluez/
etc/dhcpcd/
etc/dhcpcd/dhcpcd-hooks/
etc/kies/
etc/melfas/
etc/permissions/
etc/ppp/
etc/security/
etc/security/otacerts.zip
etc/security/drm/
etc/wifi/
firmware/
fonts/
framework/
framework/am.jar
framework/am.odex
framework/android.policy.jar
framework/android.policy.odex
framework/android.test.runner.jar
framework/android.test.runner.odex
framework/bmgr.jar
framework/bmgr.odex
framework/com.google.android.gtalkservice.odex
framework/com.google.android.maps.odex
framework/com.samsung.device.jar
framework/com.samsung.device.odex
framework/core.jar
framework/core.odex
framework/ext.jar
framework/ext.odex
framework/framework-tests.jar
framework/framework-tests.odex
framework/framework.jar
framework/framework.odex
framework/ime.jar
framework/ime.odex
framework/input.jar
framework/input.odex
framework/javax.obex.jar
framework/javax.obex.odex
framework/libmobileap.jar
framework/libmobileap.odex
framework/monkey.jar
framework/monkey.odex
framework/pm.jar
framework/pm.odex
framework/sec_feature.jar
framework/sec_feature.odex
framework/seccamera.jar
framework/seccamera.odex
framework/sechardware.jar
framework/sechardware.odex
framework/services.jar
framework/services.odex
framework/svc.jar
framework/svc.odex
framework/twframework.jar
framework/twframework.odex
lib/
lib/libXt9core.so
lib/libfmradio_jni.so
lib/libsec-ril.so
lib/Aries_EUR_Open/
lib/bluez-plugin/
lib/egl/
lib/hw/
media/
media/audio/
media/audio/alarms/
media/audio/notifications/
media/audio/ringtones/
media/audio/ui/
media/video/
media/video/shutdown/
usr/
usr/bluetooth/
usr/bluetooth/print/
usr/keychars/
usr/keylayout/
usr/share/
usr/share/alsa/
usr/share/alsa/cards/
usr/share/alsa/pcm/
usr/share/bmd/
usr/share/zoneinfo/
usr/srec/
usr/srec/config/
usr/srec/config/en.us/
usr/srec/config/en.us/dictionary/
usr/srec/config/en.us/g2p/
usr/srec/config/en.us/grammars/
usr/srec/config/en.us/models/
xbin/

sent 38653 bytes received 3128 bytes 16712.40 bytes/sec
total size is 275643161 speedup is 6597.33 (DRY RUN)