Also if you do decide on a laptop, factor in Windows 7 release in October. There are no stand alone prices out yet, but I think if you get a computer with Vista or buy vista stand alone after June, you can upgrade to 7 for $29. This is worth considering since laptops prices have dropped recently and a grande buys you a pretty good unit ATM. Have a look into the Windows 7 thing anyway.
If you can lay down the cash, good decision. Also make sure it won't affect much you do, though I doubt it can as you can run windows on them anyway if need be, but trust me, you won't want that. May as well put a virus on too . Check around to see if any updates are due to the range, from memory is September when they update the iMac?