No official confirmation yet, but there was some news post on CSNation about Gooseman not attending E3 (I believe it was E3) because he was working on CS2 (not CS: CZ which is crap and should have been dropped). I think it is logical that the big 3 (CS, DOD, TFC) will be continued on the new engine since Valve now owns all 3 (DOD was released to retail stores a month or so ago) that they will want to profit further since the franchises (especially CS) have such a massive and dedicated following. If they can pull of CS on the HL2 engine properly it will likely be the most popular online team based FPS for another 4 years (CS turned 4 years old this week).
It's a shame the developers wasted so much time on CS 1.6 which no one cares about, and CS: Condition Zero, and CS: Xbox (although it's good to get more awareness of the game out). They should have been focusing 100% efforts on building CS2.