I bought my N800 when it came out, that is early/mid January 2007. The battery has been performing as new up to about August this year, I now notice that it starts to drop a bar slightly earlier than it used to. Still quite good though. It'll be interesting to see how it's working in half a year's time.

According to a posting by someone at Nokia (developers' list IIRC), that won't actually make any difference, as the data is sent in bursts anyway.

What really makes a difference though is power-saving mode, and that depends a lot on your wi-fi router. With the one at work I can stay connected continuously all day and not a drop on the bar, with one of the cheaper wi-fi routers I own I can only stay on for a couple of hours before I have to go find a charger.

I'll second that. I switched wireless access points recently, and the one I'm using now seems to have proper power saving mode working. I didn't know what I was missing before.