I'm feeling spoiled. After years of enduring one questionable Microsoft UI decision after another, I'm having a blast tweaking and re-skinning gnome under Ubuntu 7.10 “Gutsy Gibbon.” To be sure, it's a buggy process. I've crashed X a few times and left myself with a hung shell on more than one occasion (had to jump out to the terminal and do a forced shutdown via CTRL-ALT-DEL). And I've also had my share of application weirdness (OpenOffice tends to choke on certain “incomplete” themes).
However, the reward is worth it: I now have a nice, pseudo-Mac OS X-ish UI (via the “Brushed” theme from www.gnome-look.org) with a nice, funky icon set (Dropline Neu!). Here's a link to a screenshot I took of my desktop: