I too booked through Cheapoair, they had the least expensive airfare for my MFR-DEN-PHL-ZRH flight. I mad seat selections on US Airways, couldn't do it for my first leg which is on United Express and I would have to call UAL to get the seat selection made so I didn't bother and they selected me a seat (so I am happy with that).

I check my itinerary once a month with USAirways and fortunately I did as my flight time with UAL changed (no I didn't get a call and no I don't think I would've gotten a call or notice in the mail or email, yada yada, this is passenger's responsibility... /sigh) ) so now I have to be at the airport 30 minutes earlier than I originally booked :S

Going back to the US I will not be using cheapoair only because I found someone cheaper for Berlin-NYC as I need to make stop there for an interview.

I would use cheapoair again, but only if I know I won't have to change my tickets because cheapoair doesn't allow ticket changes IIRC and if they do its $200 plus the airline's own fees so its not worth the change.