Yes, the youngest guy in class gets the highest seniority number (bad thing)...and thus the last choice in aircraft preference. Although in my class we had a number of people who bid the ATR on purpose. The pay is the same, and they wanted to be home more. Since the ATR doesn't go very far away, you are home a lot more.
As far as the ATR's going anywhere, as of the other day none were leaving until 2007, which is when the leases on about 8 or 9 of them expire. But....it is the airlines, so anything can change.
I have also heard of new hire 700 assignments. We just received 4 more, so we need pilots for them. I was in the Feb class and 6 or 7 of our pilots have already made the switch and will start differences training in the next few months.