i can only see one: eye candy.
however, if you are about to buy a new PC -- and you obviously need an OS to put in it -- go for Win7. if, on the other hand, you're talking about a PC that you already own and is currently running XP, spend your money in something else like a day out with GF (or buddies).... or buy a gadget you need. the way i see it, unless you're running Win98 or WinME, a Windows upgrade is a waste of money.
if you are bored and want to play around with a new OS, take a Linux LiveCD for a spin.
just my 2 cents....
/me happy user of Win2000 and WinXP.