for me its time, mostly. i dont have much time to browse but i try to comment in every kind here and any type of artist, not just for my friends, and yes... i have seen very amazing masterpieces WITH ANY COMMENTS INSIDE!!!! (or maybe 2 :) i dont undertands why, maybe the familiarity with other members determinate much. and every time that some user visit my gallerie and comment in any work y try to do the same just for curiosity and courtesy.