I posted this on XDA....
I noticed massive and quick battery drain and constant 3G connection once I upgraded to Froyo. This accompanied a very hot phone. After watching my cpu use and memory use I determined the Push Exchange was the culprit.
I simply turned off Push and then turned it back on. Once I reset this setting the battery drain immediately stopped, the CPU use dropped back to normal and the phone cooled off.
I think that the Update to Froyo rather than a fresh install has messed up a bunch of settings. The best thing to do is systematically go through all your apps and reset the settings...unless someone else has a better option. Also, I have been clearing all my caches and this has helped.