Autorun, by Mark Russinovich at Microsoft, gives you a complete checklist of everything that's started at bootup or login. With checkboxes that turn it off. This is worth running just to see what's in there. You may turn too much off and break something, but you can run Autorun again and turn it back on.
There's plenty of stuff worth turning off, like those useless programs that keep polling to see if Adobe Acrobat or Sun Java came out with a new version. Some of those programs are too aggressive, too. Adobe's poller seems to try to re-associate PDF files with Acrobat, after I'd changed the ".pdf" association to launch Sumatra PDF.
It's annoying that even legitimate updaters seldom schedule themselves as periodic tasks, which Windows does well and which have no overhead when they're not running. No, they have to have their own little executable in memory.