Suppose Hillary Clinton wins a huge victory tonight and manages to pull ahead of Obama in the popular vote total. I still don't see how that could possibly secure her the nomination as long as the national polling looks anything like this. The superdelegates are obviously free to take into consideration whatever they like, but I assume that anyone contemplating bucking the elected delegate totals is going to be more interested in the current opinion of his or her constituents than in months-old vote totals -- a huge share of HRC's votes came from wins on Super Tuesday before Obama's big surge in the national polls.
Now of course if there's a large lurking bloc of superdelegates with strong pro-Clinton sentiments that they're eager to unleash as soon as they're given a plausible pretext, the popular vote would be a good pretext. But given that there almost certainly isn't any such batch of superdelegates (serious Clinton fans would have endorsed her early) the whole enterprise looks doomed no matter what happens tonight.