As is my wont, I have installed the latest version of ShapeShifter from Unsanity (if you ever had interface theme fun on Mac OS 9, you'll remember Kaleidoscope --- this is much like that for Mac OS X). They recently had a theme building contest, and I have replaced my PowerBook's native Aqua theme with one of the winning entries called Digital Device, which you can see above. [The link to download the theme, however, is long since dead. —Ed. 2015-08-15]
I think the reason I fell in love with it so fast is that it's simple, not distracting, and reminds me more than a little bit of my ol' Newton Messagepad, which I really miss the capabilities of, but not so much the fact that it required an enormous, high-tensile pocket in which to carry it about. I'll likely get sick of the theme in a few weeks, as I usually do, but if you remember Kaleidoscope fondly, check out ShapeShifter --- it's quite a lot of fun.