I am seeing this issue as well, in un-modded 1.4.7 in a new world. Spawned in, moved forward. Stopped. Keyboard now does not respond inside Minecraft. Switching to another app and back to Minecraft restores the keyboard until the next key press, then stuck again.
Vanilla Minecraft 1.4.7, Mid 2011 iMac, MacOS X 10.8.2, Java(TM) SE Runtime Environment (build 1.6.0_41-b02-445-11M4107)
Russell Cook
I am seeing this issue as well, in un-modded 1.4.7 in a new world. Spawned in, moved forward. Stopped. Keyboard now does not respond inside Minecraft. Switching to another app and back to Minecraft restores the keyboard until the next key press, then stuck again.
Vanilla Minecraft 1.4.7, Mid 2011 iMac, MacOS X 10.8.2, Java(TM) SE Runtime Environment (build 1.6.0_41-b02-445-11M4107)