I can’t describe Ubuntu’s default alt-tab behavior as anything other than “utter crap.” In its defense, more recent versions have switched to the Static Application Switcher, which is much better than the absolutely horrific Application Switcher that, if I’m not mistaken, was used from version 6 through 8. However, it’s no more than a slightly fancier, and in my opinion, inferior, version of the standard Windows/Metacity/whatever alt-tab behavior, which, frankly, has been outdated for at least half a decade due to applications like SmartTab.org and KWin.
The solution, SuperSwitcher, is not quite as nice as SmartTab.org because I can’t switch applications as fast, but it does offer a nice way to easily switch between different desktops. Typing a part of the name of a window is just not as fast as alt plus a number or a letter that’s already defined. All in all, it’s the only way that I know of to get an acceptable alt-tab behavior in Gnome without using KWin or another alternative window manager.