Activision/Blizzard announced that they will be dropping development the Guitar Hero game scheduled for 2011 including any future DJ Hero games. They will also be disbanding the whole Guitar Hero division as stated by the company:
“Due to continued declines in the music genre, the company will disband Activision Publishing’s Guitar Hero business unit and discontinue development on its Guitar Hero game for 2011."
As for the future of the series, nothing is confirmed. Perhaps Guitar Hero will be back in 2012 or so but no music games will be coming out of Activision this 2011.
Development on True Crime: Hong Kong has also been stopped because it was "just not good enough" to compete in the open world genre. Which is probably why you haven't been hearing much about it for a while now.
Activision/Blizzard will instead focus on Call of Duty titles, the development of a "best-in-class digital community surrounding the Call of Duty franchise". A new Bungie IP and some new and "innovative universe with broad appeal" that will be revealed at Toy Fair later this week.
If you're all wondering about Guitar Hero DLC, that'll be done after the month of February too. All previously announced DLC will be released and that's it.