While Christine O'Donnell's upset victory over Rep. Mike Castle does turn a likely Democratic loss into a likely Democratic hold, my recollection of Scott Brown prevent me from crowing too hard. I do think Chris Coons will win this seat, but I don't want to count my chickens before they hatch.
That being said, Jonathan Chait is undoubtedly correct that the victories of (among others) O'Donnell, Sharron Angle, Marco Rubio, Rick Scott, and (we just found out) Carl Paladino over establishment-backed favorites is going to make it pretty hard for Republicans to recruit their preferred candidates into races next time around. Castle, for example, gave up a locked-down House seat for a race he never seemed that interested in running for, and which was not a sure shot (particularly when Beau Biden was considering the race). Now he's rewarded with an ignoble end to his political career. The national party simply can't be relied upon the clear the field for even its highest-profile recruits anymore.
Will this sink the GOP ship in 2010? Perhaps not -- the fundamentals are entirely in their favor, and they will still see significant gains in the House and the Senate. But in 2012 -- when, presumably, this wave will have crested -- that's when the pain will emerge, because that's when you very well could see a surprisingly large number of dangerous Republican candidates passing on competitive races for fear of being bounced in the primary season. And while they may be able to skate by on the fundamentals alone in 2010, I think in 2012 -- with the Democratic Party in full swing to promoting President Obama's reelection fight -- being stuck with a ton of subpar, far-right candidates will really come back to haunt them.