I totally understand how you feel...now. 6 months ago I would probably have said you've had to wait unreasonably long - but experience of the property market this year has changed my mind a bit. It's not that I think you shouldn't be annoyed, but the question is will you get a property any quicker if you jump ship now?
Will depend where you are, of course, but I'm guessing from the difficulties those further up the chain have been having finding a property, that your area might be one of those where there just aren't that many great properties available.
I was also trying to move in January this year - with mine sold and offer accepted on the one I wanted, and when my purchase ran into trouble, I pulled out of everything. I thought about keeping my sale happening and "going into rented" but quickly discovered that phrase is so easy to type in a forum like this, but would be a terrible idea in real life. I felt bad about screwing over the couple who wanted to buy mine, but I couldn't make myself homeless because of guilt.
I could have rented a 1-bed flat at twice as much money as my mortgage on a 3 bed house costs. I would have had to add storage costs on top of that. That's if I could get somewhere to agree to a short-term contract (but of course a contract that I didn't know how long I needed). I would have earned a bit of interest on the equity on my house, but been charged tax on that. It adds up to additional costs of 4 figures every month - on top of the fact I had sold at a relatively low price in this market. There was a very real risk that I'd quickly be in a position where I couldn't even afford to buy my old house back if the market recovered at all, let alone afford the type of property I was moving for.
You may find your vendors are in a similar situation. The choice for them may well be that if you aren't prepared to wait, they'll accept that and try to find another buyer, or chose not to move at all, rather than "go into rented". It's really not the "buyers market" people say it is at the moment, it's more of a case of a super-tough market on all sides and I think that's why prices aren't dropping dramatically.