I can't believe how much bad info is in these threads about towing with the Fit. All the hitch photos in the first page of this thread are bogus -- those are all hitches meant for trucks.
There are at least three hitches on the market in the U.S. that are specifically designed for the Fit. Go to
Trailer hitch, hitches and bike rack (800)298-8924 and do a search and you'll find them. All of them are an easy 30-minute bolt-on operation. I just ordered the Curt hitch for my Fit and plan to tow a light trailer for construction materials and maybe also a motorcycle or small boat.
As others have said, air shocks are a good idea if you'll be towing. Search the suspension forum here for info on Monroe air shocks. I've got them on my Fit and they work great. I wouldn't say they're required for towing, but will probably increase stability while doing so. But don't think they'll increase your load carrying ability, because of the way the hitches attach to the car. Too much weight will tear the sheet metal out of the back of the car. I agree with those who say it would be wise to keep total towing weight under 1,000 pounds, keep speeds down and mind your braking.
Please search other threads before posting more misleading trailering info. Most of the good info has already been presented. See this thread, for instance -- people have successfully towed ATV's, motorcycles, small boats and even other cars with their Fits:
Trailer hitch?