My two have towed very well, although I would never put their wind resistance or my gas mileage to the test against a teardrop.

We used to tow with a big Ram van, and it was actually a bit taller than the vardo was when it was folded down for travel, so the wind resistance was nil. It's a smidge taller than the jeep we tow it with now though. I imagine it's more of an issue, although it doesn't seem to slow us down much. (There are some photos of it hitched to the vehicle here.)
http://www.enslin.com/rae/gypsy/vardo16.html
We did go to the trouble of putting on a set of sway bars to keep the trailer from shimmying, but it was more of a precaution than a necessity.
They're also pretty heavy. Fully loaded, my first was about 2800, and the new one is about 2300. But for the sheer amount of trailer that we're pulling, they do nicely on the road.