Well, playable is a highly subjective term, isn't there a guy here who plays on his Quadra?
I just loaded it up for about 5 minutes, and it's playable, but I'd MUCH rather play on my 12" PowerBook 1.33Ghz G4 than on this brand new iMac, I'd estimate it to be at least twice as fast. The game is fairly responsive while playing, but selecing routes for units is a bit laggy, and map scrolling is very chunky, and that was with a brand new game. I'd hate to see how the end-game is going to perform later.
I have the 17" iMac Core Duo, with only 512MB RAM, and my additional GB hasn't arrived yet, but I'll be sure to post more when it does. I guess I was just naively hoping for a Universal Binary, since I just bought the game two weeks ago for $45, and it's already obsolete!.
Brad, if you want me to try anything, or load up a save file, just let me know. I'm not going to gripe about this, as, when I think about it, the bulk of the porting was probably done in something other than XCode, and generating a UB would probably be more work than the C3C project was, so I can understand the desire to move on to Civ 4.
It's not a huge deal for me, as I've got my PowerBook, and I tend to play Civ 3 mostly when I'm stuck somewhere with time to kill. (If only I didn't have to lug that damned DVD with me, I just know I'm going to break/scratch it to death in my laptop bag, or leave it on a table somewhere). I also have a fast PC downstairs that I use for gaming, with Civ 4 on it. This iMac is mostly my wife's machine, but I was just going through the apps that are on here to update what I can. At least World of Warcraft will have their Universal Binary patch out in the next week or so.

Now if I can only get work to buy me a MacBook Pro later this summer when Civ 4 ships...