I have 2 friends who just upgraded to CA. 1 was a 2 year F/O with Mesa in the Dash-8, the other was a 4 1/2 year F/O with Eagle in a RJ. Like many have said, it all depends on company need. From what Captains are telling me, you dont want to change seats within the first 18 months in that particular aircraft, just because you want to familiarize yourself with the plane.

Hope this helps.