Just did BOS-SEA without a stop, but we flew a bit north into Canada (not too far--we still flew over one of the Dakotas and Montana). Flt took 10 minutes extra, but since the SEA-JFK was still at the gate when we arrived, arrival time was 20 minutes late. The plane was full, but likely lots of $59 promotion fares.

As expected, on the return, took off 35 minutes late, landed 5 minutes late, due to tailwinds. A quick turn and the next flight could have been on time.