After releasing a patch for the PlayStation 3 version of the game yesterday, Rockstar has announced in their support forums that a title update for the Xbox 360 version has gone live. These are to address the login problems people have been having since launch.
They are also looking into reports that players are losing characters, rank, items, apartments and in game money during gameplay.
The game has been beset with a myriad of problems since its launch last Tuesday, and Rockstar is working around the clock to try and get the issues resolved. They have a support thread going (at the source link) that they update regularly when they have something to announce, so you can keep an eye on it if you are one of the people experiencing issues in the game