I've been using "Modify Headers" firefox addon for a while to watch US shows for research purposes, but until now I've never really questioned how it works. If you've never used it for watching South Park whenever the hell you want such research you can explore what it's about by downloading the addon here and configuring it as below:
This will insert an "x-forwarded-for" HTTP header (used by some proxies to identify the IP address from which the packet originated) with the specified value into each packet sent from firefox. Thankfully some sites, like Comedy Central, use this header to determine whether or not you're in a locale which is allowed to see their shows. This means that if you employ the hack outlined above, when you fire up http://www.thedailyshow.com/ instead of the familar "GO AWAY, BRITAIN"...
we get Jon Stewart's cheeky grin (in this case, unfortunately, accompanied by the sinister Paul Ryan):
The address I used, 126.96.36.199, is suggested by many of the sites describing how to do this. It's inside Bell Labs' IPv4 allocation and is presumably chosen as Bell are as American as Apple Pie (or at least they were before being bought out by Alcatel-Lucent) and would therefore be useful in a scenario where someone is masquerading as an American.
But is it only Americans who are permitted such unfettered access to Comedy Central's quality programming? I used XKCD's excellent map of the IPv4 space to select some IPs to use with the x-forwarded-for hack, and tested them with The Daily Show's website. The "Block" column in the table reflects the annotation it is given in the XKCD map:
Some obvious results (US companies, Canada), weird ones (Africa, Japan and Europe?) and couple of interesting entries (Multicast is OK, but Loopback and Local are not). Particularly troubling, however, is the final entry in the table. We can only hope this is resolved before word makes it to Chuck Himself...