Same problem here. Transition time between areas seems to get stabilised (around 10-14 seconds), but it takes about 3-4 minutes for the "Continue" and "Load Game" menu to appear in the main game menu... That's kind of scary !!
Except from that the game runs very smoothly, I did not encounter any performance issue so far, neither did I experience any bug yet.
I'm playing on a Mac so this is not a PC/Windows related problem. Any other mac users have the same problem ? (I mean except the problem of having a mac itself ^^)