My notebook is aging, and it's getting slower due to the upgrade of the software and the operating system (OS). I didn't change the OS but you know, you're somehow forced to upgrade it with those service pack, etc. And you will be installing some more supporting software along time, like video codec, different document viewer, application platforms, etc.
So in order to extend the life of my notebook, I tried to uninstall most of the softwares such that only the very core applications remain. I especially remove those which will be lauched upon system bootup.
On the other hand, I have narrow down the purpose to Internet browsing, word processing and a couple of astronomy related software. Therefore, much of disk space could be free up for other purpose.
In short, Keep It Simple and Stupid.