That's because the more you use your computer the more files are stored. Every time you do something, like visit internet sites, windows puts the files in a temp folder. These files that are stored build up and slows the computer down. A simple program can clean those files out and have your computer running at high speed again.
Eh, then again a lot of programs are non-standard and put things where they shouldn't go. No cleaning program is going to be able to find it then, sorry. Thats a downside of Windows, being anyone can develop for it and that it leads to crappy coding and slow downs.
However, ccleaner is the only program Ive seen thats really uptight about cleaning since its smart enough to go look through areas that certain programs use.
I disagree. If it was true, there would be evidence of it since XP has been out a while and there's people that like to decompile and whatnot. If you took 2 identical computers and installed XP on it at the same time, left 1 running for a year straight and used the other for the same time, you would find VAST differences. People customize. People install programs that autostart. A lot of programs automatically start when they really have no need to, OpenOffice comes to mind with their quick launch bs. Java checks for updates upon startup. 3rd party (Nvidia, Logitech, i.e. not Microsoft) drivers are larger and often come with programs that also autostart. Not to mention the user probably loads files such as music, movies, internet cache. You can't tell me that Ubuntu doesn't do this as well. It takes time to load programs on ANY OS.
Spanky is pretty much right about the autostart stuff. A lot of programs are picky and install services and other garbage that starts up with the computer. Believe me a lot of users don't know anything beyond the Startup folder in the start menu. Theres TONS more than just that stuff that's starting. When you start customizing Windows, you find out all this stuff.
O btw, heres something fun to do. Change the default documents & settings folder to something else. Then look at how much garbage has accumulated in the documents & settings folder that originally didn't exsist from shitty coded programs.