I just noticed that keeping a webpage with any flash component active in a window sucks a LOT of cpu cycles (and therefore presumably a lot of battery). Running Facebook and a local news page with a few flash ads in two backgrounded web windows gave me a constant cpu load of 40-80.

So if you have a lot of webpages open in their own windows and feel your N900 is slow, please consider closing the ones that have flash components and see if that makes your device snappier.

You can check cpu usage with "top". I've written a small tutorial on my N900 blog at n900experience.blogspot.com. Sorry if this sounds like spamming. I'll remove the mention of it if it offends people.