Will having two Xbox 360 consoles mean any unforeseen consequences?

I've regularly been using my Xbox Live account on 3 different consoles. If I remember correctly I didn't use a USB drive, instead I just retrieved the account from the magic of the internet. I'm not sure about what @TZHX means when they say that you'll have to re-download your account every time you switch, if he is right about that it's not something that you actually have to do, as the Xbox will do it for you. The only thing I've noticed is that when I sign on to a different console, a message pops up that says "This profile was last used on a different console."

The only downside that I can think of at the moment is that if you get achievements while offline on one console and go online with the second, those achievements may be lost. So all in all yes, you are correct it is possible and the Xbox makes it really easy for you.

I think you're largely correct -- the main thing I'd mention is that copying the profile to a new console, when you use it, it will invalidate the copy on the old console, forcing you to re-download (or "sync") it when you next connect to Xbox Live.

You can get around this by simply keeping your profile on a USB stick that you move between consoles with you.

As an additional note, having two consoles means having two power bricks, using up twice the amount of space under your TV and a second HDMI port and power outlet. If you use a Wireless controller it will mean re-syncing it each time you change between the two, if you use a wired controller it means unplugging it every time you switch.