Cillizza looked for Republican-held districts with a PVI of between R+1 and R+5, which is basically a measure of districts that are slightly Republican to fairly Republican, and listed them as possible on the table. 21 of them alone were in Ohio, Michigan, and Florida, which suggests that Clinton might have some serious House coattails.
The only logical connection between the two ideas wins across the board in PVI districts of up to R+5 and Clinton is that she won in Ohio and was on the ballot in the other two states when they had their elections with the well known consequences of making their delegates not be seated. However, Ohio according to SUSA would be won by ten points by either Clinton or Obama
It's pretty well a moot point anyhow. Even if you majored in math or miracles, Clinton simply doesn't have the numbers.
Looking at early voter turnout was one of the things which made me an Obama supporter. I think driving some Republicans to the polls just to vote against Clinton isn't going to help the down ticket races. The turnout and excitement for the race certainly does equal coattails but you need to take a good look at who the massive turnout helps. I'm not exactly sure there would be that much vigor and excitement among the old women (my sister and mother included) of Clinton's core voters.
I honestly don't see any coattails specifically for Clinton. There's certainly a wellspring of votes to oppose McCain (as well as a depressing support for McCain) but I don't exactly see anywhere near the excitement in the Clinton camp.
The argument seems to be:
Bill Foster wins in a PVI +R district.
Therefore, Clinton must have coattails.
Therefore, Clinton can help win 50+ districts.
Bill Foster won in Illinois with the help of Barack Obama (he might have done it alone as he had major help from the DNCC, but I don't know how you'd measure that). This bodes well for the coming election season (clearly) however it has nothing to do with Clinton. Good omens for the coming election do not make for some kind of specific claim about one candidate over another.
Moreover, according to SUSA and various general polls, Obama is set to win a much larger victory against McCain than Clinton would, this does actually equal coattails. There's nothing like lackluster candidate suffering an overwhelming defeat to a charismatic individual to send shockwaves through the downticket races. I think the general conclusion of Clinton's lackluster general election prospects (she'd win mind you) doesn't scream coattails.
In fact, I find Clinton's argument that she's the perfect person to go toe-to-toe with McCain another reason not to support her, not because she's tacitly advocating a McCain presidency, but because there's no reason to go toe-to-toe to a guy you can ignore and defeat while extolling the reasons why you are the man for the job. Going toe-to-toe with somebody means that you're at their level. The implicit assumption is that to bring Obama to McCain's level means that he needs to step it up a bit. Rather, to do so, Obama would have to lower himself to that level just as Clinton has lowered herself. Clinton's current strategy to advocate that she's the person to oppose McCain even though every matchup suggests that she does significantly worse is strange enough. However, when you're faced with another four years of McBush who advocates keeping troops in Iraq until they are as old as he is, nobody needs to go toe-to-toe with McCain! He is is the embodiment of failure. He's going to lose. He had a hard time beating a field of humorously weak candidates before GOP bigwigs decided he was the best of the bunch.
Also, not only was Bill Foster helped in his special election, but even in 2004 when Obama was busy sailing to victory for his Senate seat, he started campaigning for a number of house races and having his volunteers help them out. In Clinton's 2006 race, she helped nobody but herself and spent massive amounts of money in an election she was never remotely close to losing.
Further, Obama's ground game is astounding, you win big with good ground game.
Coattails? Clinton? I don't think so.