All this makes my head hurt

Thinking about communication, about speech, about catgorization - the good and the bad. The way we use language - in a personal, informal waysometimes, in a more formal way at other times. Thinking about in-jokes, about shorthand and shared family words, and that perhaps I would want to tag some of my stuff in a more personal, coded way. But then all this Web 2.0 stuff is operating in a public, or at least a social sphere, so don't we want to agree what we call 'x'? Isn't that what a common language is all about? If I was a medic, looking up the latest research, then I'd want to be sure that I was using the same term as everyone else, wouldn't I? On the other hand, looking at Library Thing just now, I was thinking of ways I could tag my catalogue records, which just wouldn't be allowable in a strictly MARC environment. Tags which would be useful for a particular sub-set of the community I serve. Hmm.