I've been having lots of fun over the past month with the B.O.B. Yak trailer I picked up at REI. The cost is kind of , esp. compared with the fifty bucks I paid for the old kid trailer I had been using for cargo. But it's worth the cost in many ways. First and foremost, it balances perfectly with the bike, at least as long as you load it right. Even with 80 lbs. of crud in a tote I can turn and move as normal, with none of the usual drag from the trailer. The problems start to arise if you load it much higher than you rear axle. Then it starts getting off balance very easily, esp. if you stop and try to park it.
Still, for grocery runs or long hauls it's been much nicer than my old trailer. In longer runs and uphill its a godsend for my legs. Has anyone else been using one?