No - we signed contracts for out first house in early July 1999 and didnt exchamnge until end of august 99 and completed 2 weeks later (on the 8/9/99 always remember that date )
Basically by signing the contracts they are ready for when everyone in the chain is at the point to exchange (most chains require everyone to excahnge on the same day and agree completion date which is normally 2 weeks after exchange, also the solicitor will require your deposit to be able to exchange!
Now your solicitor needs to ensure all your searched etc are back and then chase the rest of the chain to see where they are
I think that you've not exchanged until you've heard that they have exchanged. I think that all has happened is that you've given your solicitor everything he needs to make it happen but for exchange your vendors will need to have signed as well. My sister nearly lost her purchase after they had signed and the vendors had signed but official exchange hadn't happened. The vendor got last minute cold feet then and the whole thing nearly collapsed. But it all got sorted 48hrs later and they're now in their house.
I might be wrong in all of this so someone correct me if I am.