I stumbled upon this the other day and it works, so I thought that I'd share it.
If you use Trebuchet, the default launcher in CyanogenMod ROMs, and would like to make your app drawer background transparent, I've found that this works:
http://forum.xda-developers.com/showthr ... ?t=2187953
All that you do is flash it via recovery. If the device hangs at boot after doing that (like it did for me), try wiping the dalvik cache. If that's not enough, re-flash tytung's ROM and then do the Trebuchet zip. If you ever want or need to go back, just re-flash tytung's ROM (supposedly, the flasher makes a backup, but it didn't work for me when I tried).
Naturally, by using this, you incur a slight performance penalty over simply having a black background, but I've found that it's not that bad, even on our old HD2s.
Oh, keep in mind that you're replacing the whole launcher, so, if tytung releases a new ROM based on the latest CM source code, and you flash this over it, you'll lose any additions made to Trebuchet. When new ROMs are released, you may want to check the link above again to see if there's a newer version of the patched Trebuchet.



