So image is important. I get that. That is why so many security folks like Mac's these days. It certainly isn't because they are more reliable, but I digress.
Karmic has decent themes and wallpapers, but 8.04LTS is bloody awful. And you can't go onsite somewhere with a bunch of non-IT folks that will already be looking over you shoulder with ugly Ubuntu brown. It is bad enough that I have to use an older Dell D630, which of course runs faster than my E6400 with XP.
So the Bisigi Project has some pretty cool themes. I picked Showtime, a nice monochrome, almost but no completely OSX like theme. Next you need a simple monochrome theme for Firefox. If you have to use Firefox, Full Flat kicks ass, especially on Netbooks with limited resolution, but I swear it is faster. Lastly you need a nice monochrome wallpaper like Dark Times (after all it is Advent remember) from gnome-look.org.
And this just in, a monochrome Chrome theme to match.