i can't see you accessing premium streamed subscriber content from the usa locally without jumping through a bunch of hoops (vpn/usa cc/usa billing address). if that's what you're asking.
I recommend against getting one. Bought one shortly after they came out and it was fraught with software issues. Thought I would give it time and let them sort the issues out via software updates. Sadly the updates didn't really sort the problems out (in some cases it made them worse). You can't access any of the premium streaming content and are pretty much limited to streaming YouTube type stuff or watching what you already have on your drive. After 2 years I've given up on my Boxee and am busy setting up my raspberry Pi with xbmc to replace it.
The Boxee software is basically a fork of XBMC with added social networking and streaming of premium (paid for, mainly US only) content. Dowloaded the software a while back and ran it on the HTPC.
They have simply messed up XBMC and added stuff that is not of any use to you. If you really want to get an idea there is an iPad version from the app store as well