You shouldn't expect more than about 4.5-5 hours of "screen on" time. The phone is rated 240 minutes talk time (4 hours), and screen on while browsing or doing something processor intense like, streaming video or gaming draws about the same power, at least in my experience. If you are only getting 5 hours of off charger time, then you have a problem. With light/moderate use, you should be about to get through a full day.
Yahoo bug is resolved. I sync my Yahoo account every 30 minutes and don't see any huge data or battery draw from using it. To test, just change the account to manual for a day or two and try to sync only when you have a WiFi connection. You can check your data usage with the AT&T app before/after the the test to see how many MBs you used. I check it almost every day. And yo can sort measure your battery usage based on your normal patterns.
Sent from my HTC Surround using Board Express