Well, when I first noticed the new mamboserver.com site, it looked too drupal.org-ish to me... and it still is. Look at the sidebar, the footer, the blurbs on the homepage :)
I haven't been over to mamboserver.com for a while, but I just checked it out now to see what's changed. And you're right, it DOES look drupal.org-ish. In fact, the 'what is mambo...' blurb and the tabs are so similar to drupal.org, that I suspect they've copied us. In which case... COOL! Mambo is copying Drupal! We're being used as a benchmark for a site with double our user base! However, I agree that Mambo's site design still looks decidedly corporate and upmarket, while Drupal's site design clearly says 'community project' and 'work in progress'. I tried to think of some other sites that have similar designs, for comparative purposes, and this is what I came up with: mamboserver.com -> apple.com drupal.org -> lego.com Take a look at the pairs of sites side-by-side, and you'll see what I mean. The similarities are mainly in the choice of colour. Maybe the Drupal community should look into making little plastic toys, just as a fundraiser on the side? :-). Clean, modular, accessible, semantic, usable, and [free... err, I mean...] reasonably priced plastic toys, of course.