So, a little update. I have driven the Xterra twice now, taking it easy and watching the temp guage - about 5 miles yesterday, and about 25 miles today, both with some highway, some street. I haven't lost a drop of coolant. The areas I had seen moisture around the block are completely dry, and nothing dripping to ground. Radiator is full.

So here's a theory. My drive from work is about 3 miles, easy driving. Is it possible that during this short drive, my thermostat didn't have time to open, and once I parked, the excess heat caused a little "spew"? Not saying that I don't have a leak, but maybe just one prevelant only during high-pressure situations. If it's not dripping to ground, I'd rather not have anyone try to work on it. Thoughts?