I dont think that .fm have a market yet..
last .fm sale was O.fm in 2007-03-13 ( according to namebio ) and there is no more than 5 recent sales listed.. its not only with .fm but with most of 3rd tier TLDs like (.vg .tc .as etc... ) even .fm sounds way better than the rest.
Once i thought about invest in these TLDs and i registered some domains (pink.fm only .fm i registered) ..
High renewal prices is one of issues that halt these TLDs from growing faster.
Anyway , there are alot of domainers around who keep register and fill there stocks with these TLDs for later..