Yes, there are a few threads on this forum, and the HL Lounge forum, regarding what people are towing.
I drive a 2009 HL Limited Canadian Version with the 3.5L V6 and the tow package. Based on this, my maximum towing capacity is 5,000lbs with a maximum 500lbs tongue weight. Up until late last summer, I was towing a 2000lb (approx. loaded) tent trailer and I barely noticed it was there. I could put on cruise control and there was no downshifting happening that wouldn't have happened if I wasn't towing anything.
Last August, I sold the tent trailer and bought a 2011 Rockwood Roo 19 Hybrid trailer (high sided). The dry weight (i.e with all options installed, but none of our stuff) is 3,682 lbs. The GVWR of the trailer (maximum weight fully loaded) is 4,639 lbs. We would likely weigh around 4,000 lbs for a weekend getaway and around 4,200 lbs or so for a week long venture. I would not go any heavier than that. Keep in mind that you need to subtract (apparently), from your towing capacity, the weight of your cargo inside your truck, plus the weight of the people (with the exception of a 150lb driver...or something like that).
I've only towed my new trailer about 2,300km over a 4 day span, driving it back from Elkhart, Indiana to Moncton, New Brunswick, Canada, so I have limited experience with this (but there are alot of people on this forum with a similar setup to mine). I do use a weight distribution hitch (as do many others on this forum). When you are towing a high sided trailer, it doesn't matter if it is 2000lbs or 4000lbs, your mileage will suffer to the tune of 10 MPG-ish, as you are towing a parachute and your mileage varies exponentially with your speed.
My setup works well. The weight distribution hitch with 4-point sway control (Equalizer) kept it straight while driving between 55 and 70 MPH, even on two lane highways driving past transport trucks.
So, if you are looking for a 19' or smaller trailer that will weigh around 4200lbs with all of your stuff in it, you should be good to go. If you want something bigger, trade in your Highlander for a Tundra or F-150 or something similar that best matches up with the weight that you want to tow.
In addition, check out the RVNet and Hybrid Explorer forums (if you haven't already) and search each forum for towing
Hope this helps.