Mountain Lion sometimes hangs when mouse enters Dock – pointer is movable, but the MacBook Air seems otherwise frozen

Not a solution to the problem, but I found that closing the lid and waiting until the computer sleeps (status led pulsing) and opening it works. At least its better than a forced shutdown right?

Reading this question alongside an earlier comment from the opening poster …

Suspect an issue affecting WindowServer

Diagnosis by and of the system:

• long edition (an accepted answer)
• brief edition for power users

– in a case such as this, what's gathered by sysdiagnose is likely to include everything that's required for human analysis of the problem.

For a focused analysis, we need more detail in the question. I'll suggest an edition and maybe add a comment …