Well, okay I guess I'll start!
Got one for my son about eight years ago (son is now 14 yrs old and has outgrown it, but i still have the trailer!) and they're really fun to ride. The child can help out with the pedaling effectively under about 12 mph and sometimes I even let him pedal when I'm tired and we are going slow anyway. If the kid is a good rider you don't even know there's a trailer back there unless you're going uphill.
The only recommendation I have is, since the bike-trailer combination is very much like a tandem bike, make sure the child leans the same way you do when turning or cornering, otherwise the bike is hard to control. Don't worry, kids get used to it real fast.