Those anorexic new, super-thin iMacs are gorgeous for sure, but there's a serious downside to that diminutive depth -- the 21.5-inch iMac no longer has RAM you can replace yourself, so you're stuck with Apple's horrendously expensive prices, just like the MacBook Air and new retina MacBook Pro models. Ouch.
One thing that's been nice about the iMac, up until now, is that it's just been a desktop computer wrapped up in a slinky case. You've been able to replace the RAM, the hard drive, and other bits and pieces without issue. If you run out of space, just slap a new hard drive in there and be done with it. Likewise, there's no point in forking out oodles for Apple to stick a few extra gigs of RAM in there. Just buy it for literally half price or less, and install it yourself; it used to take just seconds.
Now, just like the MacBook Air and retinas, you're stuck with what Apple gives you at the start, so you best fork out all you can and grab as much RAM as your money will stretch to -- you always need more RAM. Or you could always just pick up a pricey, but glorious 27-incher, I guess. [CultofMac]