OpenNet Initiative provide a great starting point for anyone who’s interested in the legal implications for Internet filtering.

[…] While filtering regimes have a tremendous effect on issues such as civil liberties, international jurisdictional matters, and Internet governance, there are few established mechanisms for review and reform of Internet censorship. The paper highlights the importance of transparency, accountability, and inclusiveness in order to maintain a reliable, efficient, and global medium for communication.

http://opennetinitiative.net/docs/Legal_Implications.pdf (PDF)