From PC Magazine:

The Copyright Office within the LOC on Monday ruled that jailbreaking a smartphone - particularly Apple's iPhone - is permissible under the Digital Millennium Copyright Act's (DMCA) fair use provisions.

From Search Engine Watch:

[The Copyright Office also] granted an exemption for people remixing videos on YouTube, declaring it is not a violation of DMCA if they use excerpts from DVDs for the purpose of criticism or comment.

Read the decisions for more information.