I update my wifes 4 month old 3G to 3.1 2 days ago, and this morning it drained the battery in a matter of 30 minutes. I recharged it fully and 2 hours later, dead as a doornail. I took it to the apple store and they gave me a brand new one. I don't know if it's a fluke or if the 3.1 did something? I'm restoring from backup as I type.
Kudos to Apple for excellent customer support
Kudos to Apple for excellent customer support