The Macbook Pro trackpad is very sensitive, and this falsely triggers the Accidental Input detection in Tiger. The result is that the trackpad seems to lock up for a few seconds.
The fix is easy enough: go to System Preferences > Keyboard and Mouse > Trackpad, and uncheck Ignore accidental trackpad input. I turned that feature off and I haven't had any further problems with the trackpad not responding.
[kirkmc adds: Edited to read 'uncheck'.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060424221117409