I have always divided players into 3 categories, and these can be applied to any instrument... here it is for guitar
-guitar player
-guitarist
-musician

to me, the guitar player (or drum player etc. etc.) would be one who played around with it, but certainly had no mastery of the instrument. A player is one who plays, similar to a child, sometimes creating fantastic results, but nonetheless no master.

the -ist, guitarist, percussionist, the ist would be one who has achieved a mastery (relative to physical basics i.e. in guitar: picking techniques, dexterity, bends, physical control of instrument.) over the instruments basic techniques. One who would be a guitarist could get the guitar to do what he wants it to do, or whatever, but is still relatively inexperienced in other areas.

the musician to me would be one who would transcend his instrument(s). Music is sort of an Aristotelean ideal, a language if you will, and the musician will be able to speak fluently. (I don't mean actual music theory here, I mean as if the language is the actual music you hear.) A musician will be able to speak with their instrument, they will be able to play with others (jamming), it is a fundamental mastery of understanding, where the music becomes a part of the way you communicate, and therefore changes you (as in bilingual people).

That's a short description of what it means to me.
For further discussion I can be reached at Barefootbison@optonline.net
or at my bands website www.barefootbison.com