intrepid is still alpha, i.e. they updated the software (to make it different from hardy) and are now hunting for bugs. there still are bugs. run a stable version like hardy, intrepid at this time is just for testers that know what they are doing, it will get stable soon. but if you declared yourself as a voluntary tester and indeed found a bug, please file this bug in lauchpad to give the developers a chance to really fix it.

maybe only the X server is frozen, can you still connect via ssh or ping the machine? in this case only one program crashed another (the X client the X server, which drives graphics and keyboard). also desktop distros are by default configured to be somewhat lenient and e.g. don't strictly limit memory usage, i.e. the machine tries hard to run your program even if that means swapping or draining other resources.