I can assure you, abuse all but stopped when putting the credit card gate up. We tried all sorts of things with the trial over our 5 year tenure. Way too much

I can assure you, abuse all but stopped when putting the credit card gate up. We tried all sorts of things with the trial over our 5 year tenure. Way too much time went into dealing with abuse. In our case, it was a visual web testing service. When someone is abusing the service, another person can't use those browsers. Adding more machines might be scalable if you've raised money, but if you're bootstrapping (as we were) there's a very real ceiling to what you can afford. We were running well above the capacity needed for legitimate usage, at our expense, and still had problems stemming from Mailinator traffic. Maybe other companies have a different experience and Mailinator users turn into loyal, paying customers. In our case, they did nothing but waste resources (both computing and human). And in 5 years, not a single one turned into a paying customer, yet many were happy to leech over extended periods of time (we could see the sites being tested, so tracking it was fairly straightforward). I admit, it was weird being able to classify one whole source of traffic as simply negative, but we had the data to back it up. And just to clarify, abuse is being used in two contexts here: 1) people trying to use the service indefinitely without paying for it; and 2) people trying to actually DoS other sites, screw up our browser cluster by firing up pop-ups and print dialogs, and other general scumbaggery.