Hi
I work as a cycle courier in Brighton, England for The Bike's The Business (www.thebikesthebusiness.co.uk) and we use a variety of different load carriers:-

1. Carry Freedom trailer > we've just bought this and I haven't yet tried it with a load, but it's very nicely put together. Lightweight (around 6kg), holds 95kg (according to Carry Freedom), sealed bearings, nice people at the other end of the phone. The trailers can also be hitched together, though we've yet to do this, although it was one of the reasons we bought it.

2. Pashley trailer > not sure which model we've got, but it holds a 600mm x 800mm box, payload of 50kg. Again well built, but heavier than the Carry Freedom. Sealed cartridge bearings, same as the Carry Freedom and very strong. No problems with it yet and it's had daily use for a few months. Comes with Weber hitch which is very good.

3. Avenir Mule > we bought this because we needed a trailer quickly and a local bike shop had it in stock. Cheap trailer and good for shopping trips, but not much good with constant use. Hitch is attached to a spring so pulls back a fair bit, sides of the trailer are made from fabric, so loads press against it and can easily rub on the wheels. Steel rims rust and bearings aren't sealed. Decent runaround though.

4. Xtracycle > this is marketed as a 'hitchless trailer' (see www.xtracycle.com). This is a 'fit and forget' affair. No moving parts - holds 100kg according to website, although packing can be a bit awkward. I use mine everyday and it's a joy of an accessory, turns a bike into a true transportation vehicle. Recommended.

I notice that someone who replied to your posting has used a Bob Yak. We bought one of those and tried distributing a magazine on it. The balancing is a real issue. I imagine off-road on singletrack it comes into its own, but as a load carrier, no way.

Cheers

Chris S