The chance of a democratic takeover is very unlikely. There are 4 NOVA seats (Devolites-Davis, Cuccinelli, O'Brien and Mims) which could go democratic, but there are no other GOP seats that seem to be possible targets (this could all change if VCAP or another like group causes an incumbent to get beat by a weak candidate in a primary, etc).
As to the other side, there are only 4 possible Republican Senate pickups on the table. Chuck Colgan is widely expected to retire in '07, so that seat could be won. Edd Houck, Roscoe Reynolds and Phil Puckett also are in conseravtive leaning districts should they retire. Those 3 seats will be almost impossible to regain if their current office holders stay where they are.
I personally think the "Conservative" Republicans could regain the majority in '07 if we do not see anyone in the caucus get beat. They will gain the seat vacated by Russ Potts, and perhaps the Bill Mims seat in this special election (although I doubt it). I believe we have 9 "Conservative" Republians in the Senate: Mark Obenshain, Ken Cuccinelli, Steve Martin, Jay O'Brien, Steve Newman, Nick Rerras, Ryan McDougle, and Frank Wagner. I would also include Brandon Bell, who did not vote on the tax increase bill but is a very reliable conservative who would probably side with this group more so than the other. All the caucus has to do is gain 3 other seats, which I think will happen from within. I think a few senators will start to back the "conservatives" if they believe they gain more through doing so.
Just a thought, what is everyone else's take on it.