As far as seat locks go, expect a "possible/probable" lock on that equipment/seat for a year. What it boils down to is this:

Let's say you're hired as a Saab FO. You want to be a Q FO. If there is a Q FO position available that you want, and they are currently not hiring, you can probably slide over, one year longevity or not, provided you are the most senior person wanting that slot.

Now let's say you are a Saab FO who wants to be a Q FO, there's a Q FO slot available, but they are hiring. They are going to hire into that Q FO position and leave you where you are, unless you are outside your year seat lock.

It all just boils down to money. It takes money to transition you to the other aircraft. In the first scenario, they were willing to do it, because they needed someone on the Q, and didn't plan to hire anyone else to fill your seat. In the second scenario, why pay for two training events (your transition and the new hire to replace you,) when they can just pay for one (the new hire into the Q slot)?

All that being said, I want to emphasize to any new hires, that you are being paid the same regardless of equipment, and unless you want to be based in EWR, there is really no reason to want the Q. Take the Saab, the movement will be quicker there as there are more senior FOs in the Saab who will upgrade soon. If you are a Q FO, you will have to wait for all those FOs we hired in '08 for the Q to upgrade before you gain any seniority in your seat, which will take longer. There are a lot of '07 hire Saab FOs going for upgrade very, very soon. Take the Saab if you don't want EWR specifically.