Don't worry, it should start soon, tomorrow or the day after tomorrow. I experienced some unexpected difficulties during development.
For example, how do you refund coins if the transaction is canceled ?

It seems easy on paper, you just have to send back coins to the original sender address. But that's wrong.
If the user sent coins using, for example, an online wallet, you will maybe refund someone else : the sender address can be "shared" between all users of the service...

So the new idea is simple : I let user decides when he wants to cancel transaction and on which address he wants to get a refund.