Hello.  
My art is not stock, if I make some stock I will be sure to label it as such.  It is really disheartening to log on and see my art showing up in alot of different places I gave it no permission to be in and in some cases just plain being passed off as someone else's work.  I am usually very happy to collaborate - just send me a note and we can talk.
Unless we have talked and you have my permission in writing - all rights are reserved (except for fan art - that is not technically mine in the first place).
I guess what I am saying is have some integrity and make your own art!me integrity and make your own art!