The "bath salts" or "plant food" that is sold in headshops is mephedrone, a research chemical with a high similar to methamphetamime, MDMA, or coke.  A lot of dumb kids in new york have been selling it as "molly", and it is wreaking havoc un the UK club scene.
No one smokes it from what I know, you can just eat it or rail it.
I am the authority on this shit.  When I used to do drugs, I must have done a total of 5 grams myself.  My friend was getting it in 20gram bags for 200 bucks.
DON'T DO THIS SHIT.  My nose was fucking shot, and it only lasts as long as coke and it is super addictive.