Earlier quoted context omitted.
I think it's refreshing that Ubuntu doesn't go for the "shiny and blue" feel that Vista 7 and OS X are going for. Also, 9.04 ships with 3 community themes that are very attractive.
I don't fault them for not copying OS X like Microsoft did, but they do need to improve the default. Optional community themes don't help much because people need to turn the machine on and think: "Ooohhhh" not "Hmm, I bet I can make this look cooler if I go searching through the Preferences menu"
I remember listening to an interview with one of the original Doom developers. He said that one of the ways that they keep players interested in a game where players can go anywhere they want was by hiding secret power-ups and prizes all over a level. By rewarding a player who goes exploring, it communicates to the player that the developers want you to be interested, and that exploring can be fun.
Linux is sort of like that. You can't use all of it without exploring, so it's good to hide little customizations and treats all over so when somebody stumbles across it, they say "This is so cool!" and keep looking, learning. :)