Since I installed the 2.2 update on my Motorola Droid I have had severe battery drain issues. If I leave background sync on then the battery overheats and goes dead in less than 4 hours. Once I disable sync it seems fine, but this was never an issue before the update where I used to get almost 48 hours of heavy use out of the phone with sync set to automatic before I had to charge it.
Initially my email settings were set to get new messages instantly so I changed it to every 30 minutes and then to every hour to see if that would help. Battery life improved slightly, but I didn't see battery life anywhere near what I used to get until I disabled sync entirely. Even then I had to charge the phone 11 hours later.
I suspect there is no immediate fix for this, but I am hoping that a patch is in the works and soon.