I posted in another thread that I took my phone into VZW because my battery wasn't even lasting 5 hours (it was fine when I first got the phone, but started this on Friday). While there, I got the extended battery.
I took the phone off the charger around 4 am this morning, have had wifi on all day, and streamed Jango all day at work. It's now 9:10 and I still have decent battery left. I'm going to see how long it lasts...well, at least if it dies before I go to bed tonight. It's at 20% now, and I've had wifi on, surfed the web, texted, made phone calls and played games since being home.
I'm pleased with the battery life with the extended battery! If I can stream music for 9 hours and have wifi on, I think that's pretty good.