Ofcourse this info is taken from another website but considering the news is fuck awesome and I haven't seen it posted yet I felt myself obliged to do it myself.
No need to thank me! Well, onto the news.
Apparently, in the latest edition of Famitsu there's an advertisement for MGS4, and apparently, there's a release date on it.
Picture in question:
June 12th 2008. And considering they keep saying that the game has a worldwide simultaneous release it should be the global releasedate.
It could be a fraud though, imo it looks somewhat fake but you never know, it sounds like a reasonable date...
Source: FOK! Games