After wading through other threads on this site that claim to have solved the battery problem, and countless threads on other sites discussing the issue, here are some answers about what is going on.
Why did the 2.2 update affect my battery?
The Android OS keeps a file of information that it uses to calibrate the battery. Unfortunately, if an update to Android OS happens while your battery has a very low charge, then the data in that file is incorrect. Subsequently, the OS cannot keep track of the correct battery charge and you end up with very short battery life.
Why do some people claim they had no problem after the 2.2 update?
They were lucky enough to get the OTA when they had a full battery. Or maybe they had a 80% full battery and are affected to only a small degree. I was lucky enough to get the OTA update when I had a 15% battery charge left, and ended up with a phone that couldn't hold a charge more than 5 hours with minimal usage.
Why do so many Verizon reps claim that there is no problem?
Okay, so what can I do about it?
You need to recalibrate your battery. This involves making sure the battery is fully (and I mean fully charged), and then deleting the existing file of calibration information so that it will be rebuilt. There are many sites with explanations on how to do this, but I followed the instructions here:
You need to follow all the instructions, including step 6 to remove the file. After I did thisk my phone lasted its usual 24 hours.
What is involved in removing the existing calibration file?
That is unfornately the tricky part here; it requires "rooting" your phone. This is a simple enough procedure if you use a program that promises a simple one click root install (google it...), but it still is more technical than a problem like this should be.
Are there any other alternatives?
Possibly. If you follow the first 5 steps in the link above (which require no modifications to the phone), it might help somewhat, and I've read people claim it solved their problems. Certainly you have nothing to lose by trying it.
Could something else be going on?
Most definitely; you should also follow the usual instructions to minimze your battery use: don't have lots of widgets that update data continuously, turn of GPS and Wifi, and the rest.
Will it really work for me?
All I can say is that it worked for me, and that there are large communities of people who regularly update the OS on their phone and know that this is a common occurrence; they perform this recalibration all the time. But it is possible that something else got munged on your phone during the upgrade and that your particular problem lies elsewhere.