Same thing happened to me. After receiving a verbal "yes", I hadn't heard anything for a week. I called the REA and he said "the owners live in a different state, so it may have taken a while for the contract to arrive in the mail". They'll fax it to me, I'll fax it to your mortgage broker, then the original will arrive in the mail not long after.
3 days later, still nothing. I call back and get the same answer. 5 days later still nothing, I called the REA but got answering machine. I accused him and the vendor of holding off and hoping for a better deal (my offer was quite a bit less than asking price), the 3 day limit on my offer had well and truly past so I will be putting an offer in for a different property with a different agent the next day.
1 hour later I receive a call from my mortgage broker stating they had received a signed copy of the contract via fax - signed on the 3rd day (the final day of my offer standing), yet this was 12 days after my offer expired.
I then received a call from the REA telling me how hurt he was by my phone message, asking why I did not accept his word that the vendors had accepted, and if he had done anything in the past for me not to trust him.
Oh well, got my number 1 choice house in the end... (settlement in 3wks)