And I'll ad mine to the mix.
I bought my first trailer before my bike. Makes good sense. Just that I saw the trailer for sale before I found the bike. It wasn't until after I bought the bike and installed the towbar that I discovered the trailer never had the rotating coupling. Generally on the road it was ok but a different matter when it came to slow speed U turn's etc. Guess i got used to it after awhile. I sold this trailer a few weeks ago.
In January 2011 I found my current white Classic trailer. It's about twenty years old and has been well looked after. I upgraded the clearance and tail lights to LED and I was lucky enough to find a set of tail lights that matched the original. This trailer is a little larger than my previous black one but it isn't as heavy. I did notice that when I first picked it up it swayed a little when i was over 80kph. I put that down to it being empty and a fairly strong side wind. Tyre air pressure was a little excessive so I fixed that back to the recommended 12-15psi. It's been stable ever since.
The trailer has an interior light but until I rewire the bike I have moved the wire to the tail light connection. Also looking at installing a 12volt battery and possibly solar/bike charging system.
Under normal riding conditions the trailer is hardly noticable. Maybe the odd downshift when passing or up a hill otherwise 5th gear all the way from 60kph. Most of the time unless I have my partner on I double shift and go from 2nd to 4th with out any apparent complaints from the motor.
Nearly forgot. My average fuel usage when towing at 90kph gives about 400kms before the fuel light comes on.
Alan
I've had two trailers both without brakes. (above post)
I think the same laws that apply to cars towing trailers apply to bikes.
In SA the main rule is the laden weight of the trailer shouldn't exceed the weight of the towing vehicle and if it does then the trailer must have brakes. However, just because legally you don't need to brakes there's nothing preventing you from having a braked trailer.
Not to sure about wet mountain roads, but usually engine braking is enough to hold speed and maybe a downshift to 4th.
Dirt roads, trailer not a problem, however the bike (without trailer as well) is a different matter anything over 40kph and I feel that my bike won't handle it. So I avoid dirt roads if at all possible.
I have noticed on the Classic trailer site some spares for brakes so I would say that some of their newer trailers now have brakes either fitted or optional.
The main item is the towbar which is designed for your bike/model
http://www.classicind.com.au/ and the trailer should have a rotating coupling.
Also have read of this
http://ali-lite.com.au/2neville.htm