another good place to use naptha or wd 40, small amount on a rag will take the residue off, personally i would use wd-40

http://www.tdpri.com/forum/stratocaster-discussion-forum/73018-how-remove-pickguard-plastic-residue.html

http://www.stewmac.com/shop/Fretting_supplies/Fretting_tools:_Fret_installation/1/Behlen_Naphtha_Solvent.html