I had battery usage problems early on. What I discovered was that I had tried to download a file (podcast) that was too big to be allowed over 3G. The phone kept trying to find a WiFi connection, I guess, and kept reminding me to do the same.

When I finally cleared that task the battery life improved greatly. Like you, my wife also has an iPhone, and her battery lasted for days and days.

Like most technology, it's so complicated that I'm amazed it works half the time anyway.