Rode my longer (just over 8 mile) route today, and it went well, but now I know I need to adjust my right cleat -- it is a little too far forward for long term pedaling comfort. I also think my perception of instability with the multi-release cleat was wrong -- it performed beautifully over the course of the ride. It just releases a little sooner, which could be the cleat, or could be the way the pedal is adjusted (I think they're both on their lowest tension, but I haven't checked that too carefully -- the tension feels fine to me for now.

The best part is that I really feel like the in/out motion is very natural. Easier than getting my clunky MTB shoes (or, for that matter, my running shoes) into the toe clips/straps I was using. I'm very pleased :-)