PC and Mac game saves

I recently got a new job that will require me to travel quite a bit. I am looking to get a laptop and am thinking about possibly getting a Mac. I have never owned one but thought its a good time to give them a go. The main thing holding me back is when FM2012 comes out if I will have to get two copies for both my PC and the Mac if I get it. Im pretty sure through Steam I would only have to buy it once. I do have a couple other questions I couldn't find an answer to.

1. Are saves compatible with both PC and Mac?

2. If the same save can be played on both can it be played from a large USB stick to prevent moving from one computer to the other.

Anyone able to shed some light on these questions?

Through Steam you will only have to get it once, the limit is that you can only play it on one computer at a time (since you can only be logged into Steam with one computer at a time). Save games are compatible and can be stored on a USB stick (save/load will be a bit slower, but it will work).