The high server loads on the online portion of Gran Turismo 5 have not only caused problems with the multiplayer, but are now causing problems with the single player as well.
The single player is suffering slow downs and stallings due to “extreme online traffic congestion”.
If you navigate through the game’s menu, you can sometimes cause delays that last “several minutes”, because the title accesses servers “when starting the game and during the various screen displays in GT Mode.”
Sony has started to slowly work on these problems, starting with cutting off some access to the logs and user profiles in order to “temporarily alleviate” the problems.