TUAW reader Peter Johnson of Soluble Apps writes, "I, and a few other developers on my Facebook group, have noticed that, since yesterday's OSX update, every other run on the simulator is crashing on start. It appears to work fine when compiling and running on hardware.
I thought it could be useful for your to warn other developers to hold off from performing the update if they want to work on the simulator."
I've experienced the same issue, but found that switching from LLDB to GDB (on the advice of Tony Arnold from Apple's Dev Forums) seems to fix the problem for the moment.
Update your scheme by selecting Product > Scheme > Edit Scheme, and choose the GDB debugger for your debug scheme.
Update: Apple says no more radars are needed.
The issue occurs to a process race condition for debugserver. Instead of using GDB, you can alternatively kill your execution, wait a few seconds for the app to wrap up, and then run the next iteration.