Screenshots of the latest Windows Longhorn beta. It looks like Microsoft have one interesting eye-candy feature that Apple currently don't: the ability to do translucent elements, i.e., ones in which the pixel value can be a function of not only the background pixel but its neighbours (which allows Gaussian blurring and such). I wonder how computationally expensive this is compared to Apple's straightforward transparency; it certainly looks pretty, though.
2D gaussian blur is decomposable to a pair of 1D blurs, and you can do a 1D blur with a small kernel size in hardware on new graphics cards, which makes the process essentially free. Remember that longhorn makes some absurd requirements about how good your graphics card is? This is one of the reasons.
Demos and games these days are using this trick, coupled with a kernel size that's chosen using z-buffer information, to fake depth of field. I've also seen some very cool translucency effects (much cooler than Longhorn). All of that is possible in realtime without pixel shaders (on a GF4) but is much faster on something newer.
For examples, see Arise, by Stravaganza.
It's a neat trick, but it puts a hole in Longhorn's supposed resolution independence - the blur radius has to be bounded in pixel size, and therefore is DPI dependent. Arguably it's also pretty useless in a Desktop setting. The whole point of translucency is to be able to see what's underneath, and blurring it away just makes that harder.