One of the problems with Android devices at the moment, that are not updated to version 2.2, is the lack of ROM space. With the amount of free apps on the market, it’s quite easy to fill up that 512 Mb of space. Not every app is movable, so app2sd will list all apps you can move and show you what apps are on your SD card already.
From what I can tell at the moment, app2sd works with earlier versions of Android, but is very selective of what apps it can move. As of Froyo this functionality seems to be native, but if you are still waiting for an update, you may want to check it out.
It’s not dependent on root access, and it’s a handy way to free up some space o your internal memory.
You can check the developer site here, and of course search app2sd in the market to try it out.