I got the 14.99 Ebay battery 1500mAH and charged it last night. I didn't perform the charge to 100% - reboot and recharge. Just charged it.
All I can say it impressive! My normal routine which is to read emails, read lots of news, play some Robo Defense(battery didn't warm up like it does with the OEM DI battery) read more news, etc. So far the battery bar has hardly moved. I know from my experience the other day I would notice a good drop. I would easily say that i could get 30% or more with this battery over the OEM DI battery. No task killers, flickr sync off, and Enable Always-on Mobile is "ON". I have emails on 30 mins and Exchange 2010 Active-Sync. I get a lot of mail. Text and some phone calls. I run BuzzBox which feeds new news into the phone so its always on. I also run the Times, and a few other news gadgets. So I am constantly getting updated on news.
I am not one to hype any product but I am impressed with the battery so far. Some people have said that the 1500mAH is almost or as good as the Seidio 1750mAH battery in real world tests. I do not have one of them so I can't speak on that experience. No offense to Seidio - just giving my opinion on this battery. I hope others find it informative.
I will test it again tomorrow but I will also leave it off a charger for the night and see what kinda of drain it might have. I will report again.