Question: Recently I have not been able to test for leaks with Instruments when running apps on a device. Instruments will attempt to take a snapshot but the status will freeze at "Analyzing Process". At first I thought it was just taking it's time but I have waited over 20 minutes for it and had no luck. It does still work fine on the simulator though.

So far I have tried:
 - Using other devices with different ios versions
 - Restarting all devices
 - Updating Xcode to latest version
 - Running a number of different apps
 - Turning automatic snapshots off and trying manually

Unfortunately none of the above made any difference and I'm running out of ideas aside from reinstalling Instruments if possible.

Does anyone have any idea of what could be causing this?

Answer: 
Also had this problem after a recent XCode update, and my scheme for Profiling was set to use the Build Configuration of "Release" when it needed to be "Debug" - which allowed the analysis to complete.
Would you mind mentioning your XCode version? I had a same issue but after upgrading to XCode 4.5.1 its working fine. Also you can try one old hack - tabbing between Instruments and Xcode (it works sometimes).