The Democratic Strategist blog points to a noteworthy study on Virginia's emergence as a battleground state. Here's the study's main conclusion:
The last two election cycles have shown a significant shift in the voting habits of Virginians, making the state contentious in all races including the presidency. The increasing population of Northern Virginia (most notably in Fairfax County), and the continued evolution of the suburban and exurban vote toward Democrats (in such places as Loudoun County and Prince William County) have been essential to victories in top-of-the-ticket races in 2005 and 2006. Increased Democratic performance in suburban and exurban areas has been evident all over the country. In 2006, 16 of the 30 Democratic pickups in the House were in districts made up of suburban or exurban areas.
This jibes with the emerging Democratic majority thesis. Of course, the most recent instance of Virginia's swing toward the Democrats was George Allen's 2006 Senate loss to Jim Webb. It's important to recall, however, that Allen lost to Webb by an extremely narrow margin. Virginia may be trending blue, but a lot also depends on who is running for office. If Allen had not had his "macaca moment", he probably would have won reelection. Which suggests that a strong Republican candidate - who is up against, say, a polarizing Democratic candidate - still has a good chance of keeping Virginia red next year, at least in presidential terms.