two words (separated by a dot): default.master
having worked with sharepoint technologies since "v1" (dare i call it alpha?), those could appreciate the likes of using such rich development tools like notepad to modify themes and templates. i mean, who needs designers and other productivity greatness like color coding, intellisense, previews, etc. after all, they only save time...
as a long time fan of web development and lover of all things asp.net, i was so happy to learn early on that sharepoint v3 (i much prefer that than MOSS) was going to be built on asp.net. don't get me wrong, the sharepoint teams were able to accomplish great things with their platforms, but it just didn't lend itself to the developer used to tools like asp.net, visual studio, etc.
i also was always scratching my head on why more teams didn't leverage existing microsoft technologies to make their products more seamless...but after getting in at microsoft, i understood the big beast a bit more.
regardless, sharepoint v3 introduces asp.net as the base for the site templates. i can now use the tool (sharepoint designer) and modify the master page rather than some funky CAML that i'm not familiar with as an asp.net developer. my experience with the designer has been great -- i haven't been doing anything advanced really, but the familiarity of master pages and controls, and all that goodness brings a geeky smile to my face.
if you haven't checked it out and shrugged off sharepoint in the past because you felt it was a second class web platform...take another look...it's awesome. not to mention workflow, rss, wiki, etc. all built on the platform as well! think of the extensible possibilities!