The Word of Notch has a post about Bill S.978, which is currently being considered by the U.S. Senate: "to amend the criminal penalty provision for criminal infringement of a copyright, and for other purposes." The bill: "Makes unauthorized web streaming of copyrighted content a felony with a possible penalty of up to 5 years in prison. Illegal streaming of copyrighted content is defined in the bill as an offense that 'consists of 10 or more public performances by electronic means, during any 180-day period, of 1 or more copyrighted works' and has a total economic value, either to the copyright holder or the infringer, of at least $2,500." This is opposed by the Electronic Frontier Foundation, but has the support of AFTRA, SAG, MPAA, RIAA, and other copyright-lovers. As Notch notes, this has raised concerns that it could criminalize the simple act of uploading a gameplay video, and while it's hard to imagine such fair use scenarios becoming illegal, he offers the straightforward way Mojang would handle it should such a law come to pass:

If the bill passes, I suspect many game companies (including us) will add a special clause to the TOS specifically to allow posting videos of their games. A huge part of why Minecraft has grown so fast is the YouTube community.