I agree with everything mike said
But Lion is NOT a "major" upgrade, it is a 30 dollar interim upgrade. Both apple and microsoft usually give a "technology guarantee" that if you buy a unit after the cut off date, you get the next generation included.
One of the other guys posted that there was a june 6 cut off, but I think it will be more like june 10 when WWDC ends. He even posted a link, but the link was a bad link.
In any case, it is generally a good idea to wait as long as you can before buying a new computer. There is supposed to be a product refresh in October. If you are a college student you might not be able to wait till OCT.
Check out steve jobs sweater
http://www.vonrosen.com/#/en/221001-0900
420 euros
616 US dollars!
AWESOME isn't it!
Because he is a germaphobe, it is rumored that he wears each sweater ONE TIME, then it is destroyed, NOT given to goodwill. Take that billy boy!