Ahh ? its so bloody frustrating!
We had an offer accepted on the house we?re buying in February and finally managed to sell our property and get the chain completed early June, but we still haven?t exchanged.
We were very lucky in that that people we are buying from were happy to wait for us to sell, but that in itself upped the stress levels as they only waited for 3 months (fair enough) and then put it back on the market. Thankfully we found a buyer and they were selling to cash buyers ? great only 3 properties in the chain as our vendors aren?t buying, so should be simple and quick, right? Wrong 
Found out last week that the cash buyers aren?t actually cash buyers anymore as the first buyers were changed after two weeks, but they didn?t have anything to sell and had their mortgage in place. Found out Monday that not only are they not cash buyers, but they also have a property to sell too and no one can give us any information about the status of the person buying theirs.
Are you keeping up? 
So, the upshot is that at the point of exchange ? the top three in the chain have all signed their contracts and have no outstanding issues ? we have gone from a chain of three to four with five interested parties, one of which is a complete mystery! And our sellers are threatening to forget the whole thing and stay put if we don?t complete by the end of the month, and we?re only moving because we want this particular house ? not stressful at all 
It seems most of the problems and secrecy stems from one particular estate agency playing silly buggers and playing people off against each other and favouring those who are going to take out a mortgage via their financial services ? shouldn?t be allowed IMO. Our buyer had four people wanting to buy their house at one point and it took over a week for them (their agents) to agree on who was going to buy it ? only for it to change two weeks later.
Sorry for the long ranty post ? but I feel a bit better now!