I know one girl who was given the choice from her wealthy daddy to choose whichever macbook she wanted, ranging from the entry level white macbook to the back-lit keyboard aluminum. She chose the white macbook because it looked more like a mac, and was, from her perspective, cuter.
Of course, soon enough everyone will realize that aluminum is the new face of mac products, and people will begin to fetishize that...and we're all lying to ourselves if we say we don't like the aesthetics of mac products, be they plastic or aluminum. But anyway, I think it's just a matter of time, but for now, people still associate the white plastic with wealth/trendiness. Unless you're an early aluminum adopter, who probably thinks he or she truly is the trendy one.
For me personally, I think both have their own advantages and disadvantages, and while I like the reassuring sturdy feel of the aluminum macbook, it's not like the plastic ones aren't also sufficiently sturdy...these are expensive computers and aluminum or not, they should be last for years. This is sort of a tangent, but I'd urge anyone on the fence about either getting a plastic macbook or an aluminum one to really consider the internals of the computer, and try and fight their urge to get the latest and greatest. Now, and especially with black friday coming up, plastic macbooks are becoming an excellent value, with a refurb 2.4 white book at least $300 less than an aluminum one that is less powerful and lacks FW. If you upgrade your own memory on the 999 new white book, after sales that knock that down even more, that could be an amazing value.
However, for many people on these boards money is not an issue, and they will always pay for a new toy because a grand or two is nothing to them. But I'm not talking to them, I'm talking to the student/frugal individual who really wants to try a mac and has to scratch that itch...right now, plastic is the better value. And always seriously ask yourself if you really need a mac or if a pc will suffice...those are almost always more reasonably priced.
Ugh, sorry that got so long and preachy. The first paragraph or two was on topic!