There are probably other regular posters to this site that will have much more to say about this much better than I would, but for what my opinions are worth (and obviously my opinions are valuable, or I wouldn't have them ;), I look at PL as acknowledging the historic relationship that anarchism has had with the left, and the fact that historically most anarchists have, to varying degrees, identified within the broader stream of leftism, while also being critical of the left as recuperative and antagonistic to anarchy. Anti-left could be used as well, but without more detail might be interpreted to mean right (becasue a lot of people, including anarchists, have a hard time breaking with dualistic thinking). I look at PL as indicating having moved beyond the left, instead of opposed to the left (though I am that as well, to the extent we are going to generalize lots of individuals with heterogenous ideas and ways of operating in to a mass).
Lawrence Jarach and Jason McQuinn have some excellent stuff on PL@, such as: http://theanarchistlibrary.org/library/jason-mcquinn-post-left-anarchy-leaving-the-left-behind
John Zerzan has been more critical of the PL@ label, and instead prefers anti-left; it is a frequent topic on Anarchy Radio (http://www.johnzerzan.net/radio/),
though I don't know that he has anything written specifically about that. Another detailed explicitly anti-left critique can be found in Industrial Society and it's Future http://theanarchistlibrary.org/library/fc-industrial-society-and-its-future