Not for nothing, but "in practice" R2P has never been applied. The responsibilty to protect is a legal term agreed upon by UN member states in 2005. It provides the Security Council a legal endrun around traditional arguments of state sovereignty in cases where a country is unwilling or unable to prevent mass atrocities from being visited upon its citizens. Since 2005, however, the Council has yet to invoke R2P to authorize intervention.
Actually, as the SG's advisor on R2P Edward Luck points out, it was invoked once: Kofi Annan's diplomatic intervention in the Kenya crisis in 2008. That helped head off an alarming ethnic conflict... at least until the next election cycle, where it looks like it might be much worse despite the creative efforts of Kenyans to end the political impasse.
The problem with R2P isn't the idea, but rather the idea as understood by its more zealous promoters. When Bernard Kouchner wants to invoke R2P to invade Myanmar to deliver food at gunpoint, it doesn't matter whether that's part of the doctrine or not. Kinda like how humanitarian intervention was okay until the Bush Administration tried it. When China blocks an R2P resolution at some point in the not-too-distant future and a Western power says this is a violation of the spirit of R2P, thus allowing a military operation in the name of protection to proceed without Council approval, we'll be right back where we were in 2003. You know it's coming. It's not too early to worry about this stuff, because it's already almost happened.
Basically, I like R2P. I just don't trust anyone in power to implement it.
Sidenote: here's a good essay in pdf form from the Asia-Pacific Center for the Responsibility To Protect on the Nargis disaster in Burma and whether it was an "R2P" moment or not. The conclusion: it isn't, because natural disasters aren't covered under R2P.