How to use Firebug on your iPad and iPhone
martinkool.com
martinkool.com
I find that majority of iPad issues can be solved by just resizing safari to the iPad dimensions. Most issues I come across appear on both platforms so troubleshooting isn't too bad.
WebKit Remote Debugging[1] would be an ideal solution when it lands. For the time being, weinre[1] looks like a good (stopgap?) solution.
[1]: http://www.webkit.org/blog/1620/webkit-remote-debugging/ [2]: http://phonegap.github.com/weinre/
Souders created a nice bookmarklet a while back with I bunch of the top debugging / testing bookmarklets: