I saw this on Shacknews 1st, but loads of places since, there are lots of rumours flying about that Doom3 is in fact finished. Since most people expect it to ship very early August, I wouldn't be suprised, but this is still rumour and speculation after all.

This would seem to be what started it. http://www.gamespot.com/news/2004/07/09/screens_6102300.html?page=1

As the marketing blurb says....

we said it will be out when it's done..it's done!

My own take is that it's simply leaked marketing material, which will be used once the game is in fact finished. This may or may not be soon.