I'd almost convinced myself not to get the game -- better things to do with my time, mostly -- but then the boy got it and I have near-constant access to his computer, so I've logged a couple hours today, and over the next couple of weeks I'll probably be playing it more than is healthy.
The interface is a little clunky, but that's partially because I'm not used to it, and I've only gotten about halfway through the creature level. Though most of the advertising focused on that stage, I have a suspicion that most of the action happens at the civilization stage and beyond, so I'll reverse judgment until I've seen how that plays. I am, however, very impressed with the game manual -- it's the best I've seen in a while, a major plus for a game as varied and complicated as Spore purports to be.
If anyone reading this happens to pick up the game -- the account I'm sharing now is "medievalguy88," if you want to drop me a note in-game.