Well, here's the problem. HOW is tapping your foot " a good way to....keep time" if you CAN'T keep time playing? The YOU that is playing and rushing like a bastard is the same YOU that is tapping the foot, right? So, Dan, what's the mechanism that is making the foot's time better than the foot "owner's" time?
I'm with Ed on this one. Time has to be internal. Tapping your foot if your time is bad won't help. Spending valuable practice time working on tapping your foot seems silly. Work on playing the bass.
Doesn't mean I don't tap my foot or move my body from time to time but those actions are a byproduct of the tune grooving not a vehicle to keep time.
I will reiterate my original post though. In order to internalize time you have to listen to it. When i was in college my teacher, Earl Gately, challenged me to listen to nothing but jazz for 1 month and see how it effects my time keeping. Amazing. It helps.