Square Enix have "issued a statement" on the rumors about Final Fantasy XIII officially releasing in 2008, reading:

"Although information regarding the release date of FINAL FANTASY XIII has been reported by certain videogame websites, Square Enix itself has yet to make an official statement on this topic. Any reports of a confirmed release date are erroneous and should be disregarded. Square Enix will make an official announcement in the future concerning the release date when it has been determined."

Even though I don't believe this is an official statement it's right in saying the reports of a confirmed release date should be ignored completely as we earlier explained.

Update: Looks as though it's official.