And here's what's changed as a result of James H. Billington's tri-ennial interpretation.
(1) College professors (in general) and students (in film and media studies, at least) can circumvent DVD security measures to include snippets of motion pictures into new works for the purpose of criticism or comment for educational purposes. A similar exemption exists for documentary filmmaking and noncommercial videos.
(2) You can hack programs on your phone if the purpose is to get programs you have legally obtained to work together. This is interpreted to mean you can "jailbreak" an iPhone and load non-Apple apps.
(3) You can hack programs on your phone if the purpose is connect it to a telecommunications network you are authorized to connect to. In other words, you can hack your Iphone so it works on Verizon.
(4) You can hack a video game you own if it's just for testing or fixing security flaws as long as you don't use the information you get from the process to help folks violate copyright.
(6) If you have an ebook and all existing ebook editions disable read-aloud, then you can hack it to make it read-aloud. In other words, if the copyright owner doesn't offer to sell a read-aloud enabled version then you can break the controls that prevent read-aloud on a copy you own. Note that it seems that the publisher could offer for sale a million dollar read-aloud-enabled version to get around this. Presumably, the exception won't unravel retroactively -- the question will be was the read-aloud-enabled version available on the day you hacked the control.
U.S. Copyright Office. 2010. "Statement of the Librarian of Congress Relating to Section 1201 Rulemaking."
Wortham, Jenna. 2010. "In Ruling on iPhones, Apple Loses a Bit of Its Grip," New York Times July 26.