[Legend Android Development] dEris:
Had no issues following these steps:

Download the data2ext flashable zip from the first post on this XDA thread: Link.
Put the data2ext flashble .zip on the SD card.
Flash the zip using the ClockworkMod Recovery.
These next steps will ERASE EVERYTHING on your SDCARD! Backup now, then come back to this step.
In the ClockworkMod Recovery, select Advanced and then Partition SD Card.
Depending on the size of the SD card, pick the size of the EXT partition (1024 MB is the recommended MAX).
Swap isn't needed for data2ext, just keep it at 0
Reboot the phone.
Launch the Terminal Emulator (or use ADB (adb shell)) & type the following commands:
su
Ensure that mmcblk0p2 isn't mounted anywhere. You can do this by running mount|egrep mmcblk0p2. If that returns anything, the ext partition is mounted, please unmount it using this command in Terminal Emulator: umount /sd-ext or umount /dev/block/mmcblk0p2
mke2fs -m0 -b4096 /dev/block/mmcblk0p2
tune2fs -O extents,uninit_bg,dir_index /dev/block/mmcblk0p2
e2fsck -yf /dev/block/mmcblk0p2
tune2fs -o journal_data_writeback /dev/block/mmcblk0p2
tune2fs -O ^has_journal /dev/block/mmcblk0p2
data2ext --enable
Reboot your phone however you would like, assuming no errors from the above commands.
Once the phone finished rebooting, data2ext should be setup at this point. You can check by looking at your free space under Settings | Storage in Android. It should be close to what size you chose in step 6, but will depend on how many apps you have installed.
Restore data to sdcard (if any was backed up)

But I can't get data2ext to work. Why? Help!!

03-17 03:27:57.983: WARN/asset(1442): --------- beginning of /dev/log/main
03-17 03:28:34.313: INFO/cm(1214): Welcome to Android 2.3.3 / CyanogenMod-7-03012011-NIGHTLY-thunderc-virginmobile-Xionia
03-17 03:28:34.313: INFO/cm(1215): _
03-17 03:28:34.333: INFO/cm(1216): __ __ _ ___ _ _ __ ___ __ _ _ _ _ __ __))
03-17 03:28:34.345: INFO/cm(1217): ((_ \(/'((_( ((\( ((_)((_( (('((\( ((`1( ((_)((_(
03-17 03:28:34.353: INFO/cm(1218): )) _))
03-17 03:28:34.353: INFO/cm(1219):
03-17 03:28:34.553: INFO/mountsd(1241): Checking filesystems..
03-17 03:28:34.603: INFO//system/xbin/run-parts(1209): e2fsck 1.41.10 (10-Feb-2009)
03-17 03:28:34.633: INFO//system/xbin/run-parts(1209): /dev/block/mmcblk0p2: clean, 11/65808 files, 4467/263064 blocks
03-17 03:28:34.673: INFO/busybox(1247): mount: mounting /dev/block/mmcblk0p2 on /sd-ext failed: Invalid argument
03-17 03:28:34.673: INFO/logwrapper(1247): busybox terminated by exit(255)
03-17 03:28:34.693: INFO/busybox(1250): chown: /sd-ext: Read-only file system
03-17 03:28:34.693: INFO/logwrapper(1250): busybox terminated by exit(1)
03-17 03:28:34.705: INFO/busybox(1252): chmod: /sd-ext: Read-only file system
03-17 03:28:34.705: INFO/logwrapper(1252): busybox terminated by exit(1)
03-17 03:28:34.713: INFO/mountsd(1254): /sd-ext successfully mounted
03-17 03:28:34.883: INFO//system/xbin/run-parts(1209): Initiating Data2EXT...
03-17 03:28:34.903: INFO//system/xbin/run-parts(1209): sd-ext is not a mountpoint
03-17 03:28:34.903: INFO//system/xbin/run-parts(1209): Waiting for SD card to settle...
03-17 03:28:34.913: INFO//system/xbin/run-parts(1209): Executing file system check...
03-17 03:28:35.243: INFO//system/xbin/run-parts(1209): /dev/block/mmcblk0p2: 11/65808 files (0.0% non-contiguous), 4467/263064 blocks
03-17 03:28:35.263: INFO//system/xbin/run-parts(1209): Mounting /dev/block/mmcblk0p2 to /data...
03-17 03:28:35.293: INFO//system/xbin/run-parts(1209): mount: mounting /dev/block/mmcblk0p2 on /data failed: Invalid argument
03-17 03:28:35.293: INFO//system/xbin/run-parts(1209): Mount failed, reverting to normal mode...
03-17 03:28:35.293: INFO//system/xbin/run-parts(1209): run-parts: /system/etc/init.d/40data2ext exited with code 1
03-17 03:28:35.293: INFO/logwrapper(1209): /system/xbin/run-parts terminated by exit(1)
03-17 03:28:35.353: INFO/DEBUG(1293): debuggerd: Mar 1 2011 10:21:34
03-17 03:28:35.473: INFO/AmitDaemon(1301): AMI304+(KR3DM & KR3DH) Middleware Tester (daemon), Version:3.0.55.64
03-17 03:28:35.473: INFO/AmitDaemon(1301): Copyright (c) 2010 all rights preserved by AMIT Technology Inc.
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_fine_output.x=50 m_fine_output.y=50 m_fine_output.z=52
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_gain.x=589 m_gain.y=594 m_gain.z=600
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: gain_para_XY=128 gain_para_XZ=100 gain_para_YX=143
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: gain_para_YZ=144 gain_para_ZX=133 gain_para_ZY=158
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_coar.x=4 m_coar.y=4 m_coar.z=4
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_0Gauss_coar.x=4 m_0Gauss_coar.y=4 m_0Gauss_coar.z=4
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_fine.x=33 m_fine.y=38 m_fine.z=45
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_0Gauss_fine.x=33 m_0Gauss_fine.y=38 m_0Gauss_fine.z=45
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_b0.x=20 m_b0.y=-254 m_b0.z=-584
03-17 03:28:35.493: INFO/AmitDaemon(1301): AMID_GetCal: m_delay.x=39 m_delay.y=34 m_delay.z=43
03-17 03:28:35.953: INFO/AmitDaemon(1301): Start to Auto-Calibration!!!