Did you look at webkit remote debugging protocol? It seems they know people want a debugger for their iPad but still no real world native iPad remote debugger is available out there.
But don’t get disappointed, there is a tool called weinre that doing what webkit folks willing to do in the future right now!
Update:
By release of Google Chrome for Android phones remote debugging and tablets debugging mobile web apps is no pain anymore. You will need an expensive Google Galaxy Nexus phone with ICS on it to do it. But future is bright! Check out the video demo here:
weinre is Web Inspector Remote. Pronounced like the word “winery”. Or
maybe like the word “weiner”. Who knows, really.