I like Aero. It makes Vista slick and pleasing on the eye. But it puts more load on the system which is fine when attached to the mains, but when I'm running on battery the eye candy can contribute to less runtime that I'd like.
In Vista it's easy enough to turn Aero on and off, but it's a pain having to remember and wade through menus to get there every time.
It was really cool to discover a little app that sits in the systray and does it all for me - check out Clints Vista Battery Saver.
What's really cool is Clint released this as open source and folks have already suggested some neat changes which he's taking onboard so expect this to get even cooler over time...
Update: I made some changed to the app to include some of the other suggestions and sent them back to Clint. Because he's cleverer than me he integrated them in a much better way and didn't break anything, so check out his new version.
Update: Tamir from MS has now made a fully logo compliant app that controls Aero and Sidebar to save precious ergs... Doesn't let you turn it back on on-demand though (yet)!