McCauliffe only being up by 4 in the last PPP poll (probably in the ballpark, given that it's PPP) seems like cause for concern.
VA gov races are always in an off-off year (no prez, not even any congress) but we have had a decent Dem record recently despite that turnout depressor, and despite the last election. (McConnell, whose campaign was largely about claiming to be a northern VA moderate)
Cuccinelli is a lunatic... but he was also a lunatic when he won the AG race 4 years ago.
McCauliffe, unlike Warner or Kaine, doesn't have a track record of winning elected offices in Virginia. He will, I suspect, do unusually poorly in the conservative parts of the state because there's no loyalty or personal angle. He's just the guy with a D by his name.
Unless McCauliffe blankets NoVa with ads so scary that they will be decried by inside the beltway fainters as in bad taste I see Cucc probably winning.
Will Hillary (and Bill) campaign for McCauliffe? Might help.