Right now, this is a web ad:
It's not going to stay one: it's actually 90 seconds and has the McCain "I approved this message" added on, which means that (as Ed notes) you should expect to see it in TV ads pretty, pretty soon. Ed also notes that this is going to guarantee that we're going to hear about it in the debate: Obama rather publicly challenged McCain to say it to his face, and I think that McCain will be rather happy to oblige him.
Moe LanePS: I understand that certain Obama activists have been programmed to squawk "Keating Five!" whenever the word "Ayers" comes up. Anyone who chooses to do so in this thread must include this sentence, word for word, with the link, and with no attempts to warp the meaning:
"Of course, this attack is hypocritical of both me and Senator Obama, since the Senator is happy to let fellow Keating Five member John Glenn campaign for him in Ohio."
Thanks in advance!