It's not going away, and it sounds as though you're about to hear an awful lot more about it. Newly formed Scottish developer Ruffian is most certainly working on a new Crackdown game, says "rumour" today, and apparently it's scheduled for the end of 2009 or early 2010.
The project's being called "Crackdown 1.5" in the UK trade, and it's set in the same city as the original Realtime Worlds 360 classic. Multiplayer's going to play a massive part in the game, aparently, moreso than the new single-player stuff.
Just a hunch: you might hear more about this... tomorrow. Life on the edge, and all that.
Realtime Worlds put out a statement at the end of December saying the firm was in ongoing negotiations with Microsoft about continuing the franchise as a reaction to rumour that Ruffian had picked up a second game.
Ruffian - the Dundee-based developer comprised largely of ex-Crackdown staffers - was confirmed as open in late January.