Devil in the detail
The devil is in the detail (and in the courts' interpretations).
What is "circumvent"? Is DRM circumvented if one sticks a microphone to an earphone and tapes what comes out of an iPod? Or uses a cable to connect the headphone output to a recording device (for personal replay on some other player, of course). Or opens a DVD player and moves the region jumper?
At the other extreme is someone cracking complex encryption schemes and then selling keys to unlock (say) encrypted pay-for movie channels, for personal gain.
I'd like to see a definition that notwithstanding anything else, no circumvention ever takes place when a person causes a signal intended to emit from one device to emit from a different device, provided that he has the legal right to listen to or watch the source and the legal right to use both devices, and is using his chosen output device personally and not for profit. IANAL but I think that covers most "fair use".