This post at the blog connected with the journal The American Interest [hat tip: DPT] argues that 'the responsibility to protect' (R2P) is a "nebulous norm". One way norms get less nebulous, however, is by being invoked and debated, as Badescu and Weiss suggest in a piece in last November's International Studies Perspectives (abstract here).
According to them, R2P should not be seen as synonymous with humanitarian intervention by military means (too narrow), nor as synonymous with human security generally (too broad). Rather, R2P is "about taking timely preventive action, about identifying situations that are capable of deteriorating into mass atrocities and bringing to bear diplomatic, legal, economic, and military pressure" (p. 367). Given the speed with which the Libyan situation unfolded, an argument can be made that there was not time to do these things in sequence -- i.e., first the diplomatic and economic, then the military measures -- but that, rather, an effective response required a deployment of these different means pretty much all at once. That, at any rate, seems to me to be the most plausible argument that the military intervention and accompanying actions (e.g., freezing of assets) do represent a legitimate application of R2P rather than a misapplication. It will be interesting to see how Pres. Obama frames the issue in his address tonight.
P.s. After listening to the speech, I realized that my reference (above) to the measures being taken "pretty much all at once" is a bit of an overstatement; the asset freeze etc. did precede the military action -- but not by a prolonged period. As Obama noted, the entire sequence of events from the start of the Libyan protests to the intervention took only 31 days.