Hi Lory, I think A2K itself is an experiment in Folksonomy, but I can't say that I know the results. The moderators here might have a better feel for how the socially driven tagging process is working.
I find that I don't use tags much any more to look things up because they cover too wide a range of possibilities. Instead, I tend to use tags just to mark threads which I may want to review later (even though I try to apply relevant tags).
Prior to the tagging system on A2K I used to click on certain "forums" which were my primary interest and rarely looked at threads which occurred in other categories. Now I tend to review all threads which are created and either thumb the down because I'm not interested (and want them out of my list), or classify them (because I want to review them later), or simply ignore them (leave them in an unclassified state).
I suspect that a socially driven tagging system would be more effective in a very large community where irrelevant tags are pushed out by the bulk of the other tags. So social tagging may be better suited to large scale structures like the Internet itself. But those are just speculations. I haven't studied this at all.