damn... if i had gone to work on monday i coulda told you sooner.

yea basically if you want to constrain to 2 dimensions you ctrl + click on the arrow you don't want things moving in... i've found that if you want to undo it, you've gotta ctrl+click inside the yellow square. haven't tried it with rotate or scale yet, but it is kinda handy if you want to move a vertex fast but make sure it keeps on the same plane. i use it a lot because trying to drag around in the perspective view can potentially give you some unwieldy results unless you constrain.