In most states, a vehicle with a salvage title means that an insurance company declared the vehicle a total loss, and paid the insured for the loss of their vehicle, not the damage. As far as I know, most insurance companies will declare a damaged vehicle a total loss if the cost of repairs is greater than ~60% of the actual cash value (what a dealer will pay for it).
So if you have a car that's only worth $500, and it get's keyed down the side (probably $300+ to fix properly), that car would most likely be considered a total loss, and thus get a salvage title. (if you accepted the insurance claim) That example is extreme, but I'm sure you get the point.
If you have a S2000 thats worth $14000 to a dealer, and it gets $9000 worth of damage, it may be considered a total loss, and thus get a salvage title. If someone just rear ended a S2000, and ruined the trunk lid, both rear fenders, tail lights, muffler, etc, I would assume that it would cost more than $9000 to buy genuine replacement parts + installation + paint. In this case, it's a good chance that this S2000 would be considered a total loss by the insurance company, thus receiving a salvage title. However, in this example, it's unlikely that the drivability of the car would be affected, and buying this vehicle would not be bad at all.
Also, body shops are businesses, as I'm sure you are all aware, and they do not make any money if an insurance company declares a vehicle a total loss. So they will try to send the insurance company a low ball price quote so that they can earn the approval (and money) from the insurance company to go ahead and fix the vehicle. If they do fix it, this car will still have a clean title.
So, a salvage title does not automatically mean that a particular car is junk, because a car with a clean title could have the same problems / history.