I think some agents are only able to check-in one person at a time. Almost everytime five of us try and check-in together, the agent goes into a frenzy at the prospect of having to process multiple passengers at the same time. If I am alone, check-in will usually take 3-4mins. If there are 5 of us, it will often take 6-7 mins per passenger.

Just recently - I sat at check-in at Dubai airport for 30 minutes (3 of us traveling) I have no clue why it took so long, but the agents seemed totally confused.

Cheers,