According to maclife, Mac OS X 10.6.4
"Resolve an issue that causes the keyboard or trackpad to become unresponsive "
http://www.maclife.com/article/news/appleseeds_fourth_mac_os_x_1064_beta_contains_no_knownissues
Freezing Problems On 2010 MacBook Pros
HardMac's Lionel reports that a reader with a MacBook i7", 8 GB,500 GB HD, says his "small but pretty jewel" will freeze making it impossible to use the keyboard, eventually blocking completely, requiring a complete restart of the machine, and that after some research he's determined that the problem seems to affect a great number of core i5 and i7 machines.
I'll add here that I've been experiencing somewhat similar issues with my late 2008 model 2.0 Ghz unibody MacBook, and it got a lot worse after installing the OS 10.6.3 update, to a degree that I finally got sick of having to reboot two or three times a day to restore keyboard response, and reverted to OS 10.5.8 in disgust.
Apparently this is a known issue with Mac OS 10.6.3. appletoolbox.com reports that users continue to experience intermittent mouse/keyboard freezes and/or system stalls after updating to Mac OS X 10.6.3 -- typically the cursor freezing in place, or text input becoming suddenly interrupted then catching up a few seconds later. Personally, I mercifully haven't encountered system stalls, and the mouse/trackpad have always working long enough to permit saving work and shutting down applications in an orderly fashion before rebooting.
According to appletoolbox.com, factors that can trigger this behavior with Mac OS X 10.6.3 include Adobe Flash, Spotlight problems, outdated drivers, and problematic startup/login items. On my rig, it seems to be mostly associated with switching between Desktop Spaces using keyboard commands (it's never happened that I can recall when using the Spaces menulet).
Appletoolbox.com suggests that the most effective workaround is a downgrade to Mac OS X 10.6.2, but say they've received word that forthcoming Mac OS X 10.6.4 includes new IOUSB files that should resolve the freezes/stalls under most circumstances. Here's hoping.
http://www.macprices.net/cell.shtml