@jBelkin
Sorry, but there is no such thing as XP2. I suppose you mean XP Service Pack 2? And, you statement is completely false. I have a few friends who installed new versions of the Mac OS only to discover that their computer could not handle the additional strain. Yes, like many other operating systems, new versions MAY increase performance (Windows does this with Service Packs), REAL upgrades generally take up more resources.
On another note, it IS NOT cheaper to own a Mac over the long run. If you buy an iMac and want to upgrade it later, you're in for a rude awakening. Sure, you could sell it and buy a new one, but I could simply upgrade a PC for a fraction of the cost. In fact, I can build a system comparable to the most expensive iMac on the market for $900 less (I did this for a friend). That system will be completely upgradable in the future should he need a performance boost.
Please, support Apple for the right reasons. Don't try to make new reasons up to justify your decision.
The Amazing Resale Value of Your Mac