In the Console view or the Inspector, if you double-click on the current value displayed under the Volume fader or a specific part of the Sends' Level/Pan knob, a white box appears and allows you to enter a desired value, which is very convenient. But double-clicking on the current value shown under the big Pan knob does nothing.
Also, the Sends' Pan value entry box isn't really useful, because, for example, if you want the value to be set to 50% R, you have to enter "95." I think it should be set to 50% R when "50" is entered and to 50% L when "-50" is entered (EDIT: Actually, I didn't know I could just enter "50R" "50L". See Kevin's post below)