Although retail listings for video games are rarely accurate, I feel it's worth noting that GameStop, in Germany, has listed Grand Theft Auto 5 for a January 15, 2012 release. Don't mark it down in your calendar, though. Often, retailers create records for games they expect to see in the future, without having much concrete information, so it's more of a projection than anything else.
I predict, though, that we will be getting a fat Grand Theft Auto 5 announcement at E3 in June, and you can mark your calendar for those dates: June 7-9. We'll be bringing you all things E3 here at G4, as we do every year.