[Desire Q&A, Help & Troubleshooting] TjPhysicist:
If you want full apps on your sdcard (using ext) then you have to do this:

format to ext using the recovery, i used amon_ra, so im not sure how well and which version of clockwork recovery works well etc. I did 1GB=ext3 rest=fat32. Windows7 does not recognise the ext3 partition and always comes up with an error when mounting the card with "ignore error, fix error"..ignore error works perfectly well.

You need a ROM that has the scripts that allow this to happen. As such, afaik, it is a very minor detail/fix, but your ROM needs to support it. AFAIK, SupervillainHD and Defrost support this, I have not tested any others. Any ROM that says a2sd+ should support this method of a2sd, if in doubt try it out. There is no menu option, no extra thing to do. It will automatically detect if you have an ext2/3 partition on sdcard and do the moving on the first boot. Be aware that Cyanogen does not support the ext3 method of a2sd and only the crappy froyo a2sd. I believe there is a fix, but it sounded kinda hackish to me, and a lot of people in #cm seemed to have a bad opinion of ext3 a2sd (as opposed to the froyo's inbuilt a2sd).

The easiest way to test it out is to adb shell (or access root shell from the phone), and type ls -l /data/app*. If a2sd is on and working you should see something like this:

lrwxrwxrwx root root 2010-12-02 14:48 app -> /system/sd/app
lrwxrwxrwx root root 2010-12-02 14:48 app-private ->/system/sd/app-private

if note you should see:

drwxrwxrwx root root 2010-12-02 14:48 app
drwxrwxrwx root root 2010-12-02 14:48 app-private

Note that depending on ROM/phone setup the part after "->" can be /system/sd-ext/app or /sd-ext/app the point is there should be a -> and something after it, and the first letter should be l (for link) and not d (for directory).

N.B: As i said, and I am sure you are aware, Froyo comes with a built in semi-a2sd thing. this version does not need you do anything extra. Merely go to the Menu in any CM based ROM's and click on CyanogenMod menu (or some other extra menu you're rom may have put in) and select "always enable external storage of apps" or something similar (whatever option in there sounds like it). This is a hackish way of doing it.

The proper way would be to go to menu->application->manage applications and select the app you want to move after installing it, and click on the "move to sdcard" button.

This is built into the android system, with more security features or smthg, but is a little lacking. Unless you use the hackish method (which is not always reliable afaik), the dude who wrote the app has to enable support for app2sd via this method in his app, not a lot of people do. But most big games and such do so. Also, this method only moves parts of the app to the sdcard. The biggest disadvantage is that the apps are stored in the fat partition, which means mounting the fat partition onto the computer (by clicking on "mount sdcard to computer via usb in the pull down bar") wil disable and render useless any apps that are on sdcard (until the sdcard is mounted back into android)...and widgets go haywire on reboot, since the fat partition takes a bit to come online (due to the checks the system does before mounting it). These issues do not occur at all with a seperate partition that is ext2/ext3.

-Tj