Bump for answers to original question... I would love to be able to turn 3G off when in areas of poor coverage. Running 2.2 Jrummy(Kangerade).. if the option is there, I dont' see it...
Menu > Settings > Wireless & networks > Mobile Networks > Data Enable/Disable
Also OP if all you want out of 2.2 is the ability to turn data on/off to stay under 50MB for the month I might suggest you to just root your phone and get a free app in the market called DroidWall, it gives you the ability to set what programs are allowed to access wifi and 3g data
I think you would enjoy 2.2, as I love it and would never go back. But if you dont need it or dont care to have it I think it would be safer to just get root and use DroidWall and skip the flashing ROMs and what not.
This is the guide I used.
Guide to Rooting Android 2.1 on a Motorola Droid | Droid Life: A Droid Community Blog
As stated it will void your warranty and there is the possibility to mess your phone up but as long as you follow the directions you should be fine