I use one account on 2 360s in my house but you will either need to recover your gamertag when switching between the two or just swap the hard drives. If you are going to play campaigns and stuff like that you may want to do the latter because all of your progress will only be on whichever hard drive you were playing last. Recovering the gamertag won't transfer how far you've gotten in a game.
I also remember having to do one more thing when I first got my second 360 but I'm not sure what it was called. I had to go online and sort of "register" that console in order to get all of my DLC on there. It was a new Arcade and I was using a 60 GB HDD that I got from friend after he upgraded to a 120. I don't know if that had anything to do with the extra step I had to take but it was a simple 5 minute thing to do either way.
As far as what one poster said above about only having to recover your GT once, this is not the case. If you are going to be taking the recover route then you will have to do it every time. Unless someone here can give a good reason as to why you wouldn't want to, I think you may want to just detach the big ol 250 and slap it on your old 360 when you want to switch.
I LOVE paying for Xbox Live! I also love that my love for it pisses off so many people.
