common check-in is a good idea, but not with a manual check-system.
I dont think that the lines of pax waiting to check-in would get any shorter by using a computer, the amount of pax waiting in line is due to the masive operation that ryanair have at Stansted.
I have checked in for many Ryanair flights and have not had to wait longer than anyother time with other airlines who used computers.
I stick to what I say, If a agent has only ever done manual check-in they are good at it and it just take the same amount of time as using a computer, Remember Ryanair only has 2 agent on each flight most airlines have 3 agents the check in's are open about the same time and Ryanair's aircraft seat more pax as lets say Easyjet who sometimes pull over the pax from another flight.