Thanks for the quick replies! There was no odor from the smoke, even when down on my hands and knees looking under the car I didn't smell anything unusual. My engine oil and ATF levels appear to be okay, however if there is a leak somewhere, I suppose that only a few drops on the exhaust could cause smoke, but not a noticable drop in level. If this problem is "just" a fluid leak somewhere, I suppose it would be okay to drive to the shop, rather than towing. I'll go check for drips under the car...