[quote name='nasum']So your profile doesn't automatically update across your 360's? That's weird, but I figured I'd probably use the USB stick method anyway.[/QUOTE]
No, if your gamertag is saved on the HDD, then each time you log on with the other console (whichever one you did not use most recently), it would force you to recover your gamertag to update it. Pain in the butt because it takes several minutes and lots of typing (email address, password, etc). MUCH better idea to save your gamertag on a USB memory stick, and just move it from room to room. Important to note that you can't be online on both machines at the same time with the same profile.
I do have two of them at my place. I bought the second one mostly as a spare when Target ran that incredible $80 after gift card deal on the old arcades right when they announced the slim. I have on occasion used both at the same time (with two different gamertags) to do some "local" online co-op or boosting on two different tvs. I don't use the second one often, but it is nice to have.