After downloading and using the new 64bit client for Mac I noticed that the keyboard would stop working at random times and would require a logout and client re-launch.
I switched from full screen to windowed full screen or even just playing in a window and since then no keyboard issues. Worth a try if you having the problem.
MacBook Pro (15inch , Early 2011)
2 Ghz intel Core i7
16 GB 1333 MHz DDR3
AMD Radeon HD 6490 256MB
Intel HD Graphics 3000 512MB