Okay, this morning we've got a couple sites, in this case Xbox365, quoting EuroGamer, saying that Halo 2's release date has "slipped" to April of 2004. EuroGamer cites Microsoft as the source of the information, but there's no official press release text or link to one; in the Microsoft Game Studios Press Site, there's no mention of this "information". Eurogamer claims this is a delay of two months.
Everyone who watches this space knows that the only thing that was officially ever said about Halo 2 was "in 2004". If you want to interpret that to mean January 2004, then sure, I guess releasing in March means a two month delay. But you can't have a delay of an unofficial release date; and frankly, anybody who thinks about it for two seconds would probably assume that if Bungie knew that far in advance that it was impossible to release for the Christmas 2003 season, that the delay was probably going to be more than just a few weeks, so assuming January was probably wrong in the first place.
It's also unclear whether or not the dates in question are intended for a European audience; that seems to be the opinion of the Xbox365 forumgoers, anyway.
And of course, at the end of it all, there's horses' mouths and horses' asses; Microsoft is a big company, and it's probably better to trust those who are closer to what's going on.
UPDATE: Microsoft's official Xbox.com game list still lists the release date for Halo 2 as "TBA", although the page for Halo 2 itself does, in fact, say March 2004.