I don't know why everyone argues about whether to wait or not to get their new computer. It's either you need it, or you don't need it. If you already currently have a computer that serves its general purpose right now, wait until August for the back to school discount on the Mac Books.
However, if you absolutely need a computer right now *namely a laptop,* go ahead and buy it. You won't be sorry that you did. The only suggestions that I have are to possibly buy a refurbished product if you don't mind not getting the new box. It's a great savings! It gave me an excuse to drop 80-100$ on the 4 gig upgrade for the RAM. I bought this Santa Rosa, 2.2 ghz white MB when the Penryn ones came out. I got a huge discount considering the not so big of a performance upgrade between the new revision.
As far as the aluminum goes, it's either you like it, or you don't like it. There's been so many of these threads that my eyes are sore (not to mention how boring it is to see them popping up over and over again). I know this is a rumor site (lol) but how many times can you beat the bloody corpse, that is, whether or not Apple's going to update the stupid MacBooks.
The point is, NO ONE knows or has any conclusive rumors about the aluminum updates, or even an imminent update at all. And I completely agree with the people referring to the fact that Apple only reveals like Mac Pro and Xserve updates at WWDC usually.
Cheers.