I have also had savegame issues, hit 510 population on sandbox mode and saved. Could not reload the game. All other saves have reloaded. I realize that a game of this complexity might take some time to ID all the issues before a patch can be issued. I can wait.
However, another issue came up. My disc is apparently flawed, likely during manufacturing process. There is an odd line going from center of disc towards outer edge that I did not notice before (not a crack or scratch anywhere on the disc). It will now not load not matter what I do. I take very good care of my 360 and all discs - every other game I have (over 25) are still playing fine. I have set up process to send it back to Amazon for a new disc, which they say they will be sending. Kind of a pain, but glad that Amazon is being cooperative. Never had any game do this before, pretty odd.