Techniques for profiling memory in Safari desktop and iOS?

When you install the iOS SDK, a utility named Instruments is also installed. It can track all sorts of usage stats, including memory (there is even a "Leaks" template). The great thing is that it can track both the iPhone/iPad simulator and any connected iOS development device. It also, of course, can be used to monitor memory usage in Mac OS, so it may help with Safari as well. You can find Instruments in /Developer/Applications.

Something else that is handy is that whenever you sync your iPad/iPhone with iTunes, it also syncs any crash reports from the device to your computer. They can be found at ~/Library/Logs/CrashReporter/MobileDevice/[Device Name]/.

One thing we found when developing for the iPad in particular was that it was very prone to crashing due to memory issues, particularly in image heavy applications like ours. One thing we learned was that just removing a DOM element does not mean that element will be garbage collected by the browser. We found that setting the image src (or background-image, if it was a div) to an empty string before removing it from the DOM helped immensely.

Not sure if any of that helps, but hopefully getting Instruments up and running will give you a better idea of where all that memory is going.