Well, radio, for one, will probably say he cannot get stoned...at least not on their airwaves. It will be very interesting to see what radio stations will play the tune without bleeping out the word "stoned." We don't think a song has repeatedly mentioned pot smoking so much since Afroman's 2001 "I Got High" We're in a much more conservative time than we used to be. if Mayer had put this tune out in the '70s, no problem. Now...not so much. Can you imagine what would happened if Eric Clapton put out "Cocaine" in 2009? Zac Brown Band is getting bleeped for the word "ass" and the line "roll a big fat one" in the song "Toes." However, the words "beer" and "tequila" are still just fine.
As far as the song goes, "Who Says" is a low-key acoustic, stripped down tune that is only Mayer's gentle voice and a guitar for the first two-thirds. It sounds very Paul Simon from the "Hearts and Bones" era with a reflective, chugging mid-tempo lovely melody.
Lyrically, Mayer goes through various scenarios of what he might do while stoned: go to Japan alone, drunk dial an old girlfriend, etc. Of course, the line, "I don't remember you looking any better/ then again I don't remember you" might kill any chance of romance there.
(Also: try to hear the "johnmayer.com" shout-out right before the first chorus.)
The only question is was he stoned when he wrote it and recorded it?