Of course at the end of app development it's bug season. Testing on device is a big deal with some of these problems because they only happen on the resource-restricted device. Testing on device is everything when it's a mobile-specific web app.
In the past we've used various add in tools but with iOS6 it's all built in. Here are some notes helping remote debug from desktop to usb connected phone.
Safari 6 comes with "Mountain Lion" 10.5, but I'm on "Lion" 10.4 and the Safari upgrade doesn't appear to be automatic – you know how Apple likes to force upgrades. Easily worked-around, however, as Safari6 is hosted on Cnet here: http://download.cnet.com/Apple-Safari/3000-2356_4-34119.html