I've seen a few of these tumbling services turn out to be scams. I guess that's the nature of the business.
Never used a tumbling service, but if it's true that it's a scam or it turn out to be, cryptocurrency users will most likely avoid services like it, and use Zerocoin or Dark Wallet for making anonymous transactions in the future.
I guess it's a similar predicament to tor marketplaces. Some start off or appear legitimate, but at any time they can take the money and run.
Is Zerocoin a new coin or something built around Bitcoin?
Zerocoin was a proposed add on to the Bitcoin payment network, but it was modified to be its own Cryptocurrency. Google "Zerocoin" or "Zerocoin Project". Zerocoin's purpose is to make transactions completely anonymous.