Just to close the thread as i was the OP.
We found the lounge (on the third try!) and was pleasantly surprised. It cost the equivalent of £24 and for that we got a very comfortable place to relax for the 5 hour wait.
O Good food/drinks including a quantity of quality sandwiches, soup and cakes
O 5 internet terminal (No cost)
O Quick WiFi
O Shower
O Ample comfortable seating
On short connections: The Qatar staff were very efficient in directing connecting passengers (under 60 mins) to the "fast lane" of security. However in all honestly we were through in 20 mins using the regular line (all machines in use - this is not BAA!)
There is quite a scrum to join the security queue - as the entrance to the zig zag queuing area is relatively narrow. This gives the impression as you enter the area of a long wait time but this is not actually the case.
Smala01