When you leave the menus and enter a race, it looks as if the loading screen gets stuck and nothing happens. However, the initial loading just takes a very long time - it might load correctly if you give it some time (half a minute or so).

After this first loading of in-game data, loading times will become fairly acceptable while the game is left running. Loading is slower than on a version one Xbox though. If you turn off the game, the next time you run it the first loading of in-game data will again be slow.