My Definitions:

Sub - voluntarily gives up like 90-95% of all control until something bothers them to their Dom.

Slave - gives all control and obedience to their Master.

I am a sub. The word 'slave' has always bothered me. I guess it's because of the usuage in our history. It's always been negative when someone said it. It's hard to think of something good like the word "Slave." Also the master/slave relationships I have seen just have me saying "they're going to far." (i.e. punishing while good friends, who know about their relationship and are into bdsm too, are onlookers.)

That's my two cents.