I caught the John McCain speech on MSNBC and, based on their camera angles, it was hard to get a sense of exactly how many people were in attendance--or how the speaking venue was arranged. But it sure sounded like a pretty small crowd of partisans--maybe a hundred or two hundred people--trying very hard to sound like a big one.
Of course, the ability to attract large, boisterous crowds is only one metric of political strength--and a potentially misleading one at that. (Otherwise, Barack Obama would have locked up the nomination long ago.) Still, it's not a completely meaningless indicator, either. And I'm hard pressed to think of the last time McCain generated anything even remotely resembling the kind of enthusiasm that not just Obama but, at times, even Hillary Clinton sparked on the campaign trail.
Admittedly, I've caught only a few of his events in person, so I'm relying heavily on my impressions from media coverage. If commenters (or others) have counter-examples, please let me know...