PC users tend to install more things to "try out" and then uninstall.... these leave traces behind that can clog the PC. If you use a PC and run XP, it is recommanded to install this:
http://www.ccleaner.com/
CCleaner cleans the XP OS so you'd regain some space and more importantly have a leaner registry....
ANyway, I am using both PC with XP and Apple with OSX....
PC is more value for money when it comes to raw power. Apple OSX is not bad too. Its really Apples and Oranges...
If I go out, I prefer to bring along my Apple - its white and looks presentable...
At home, both has its advantages.... like I said raw power to the PC. Esp if you slap a good graphics card on it.
so, that's why my PC boot up time is getting longer and longer