Recently, I noticed that some of the sister, stack exchange sites use tag suggestions when composing a question. I found this to be a rather convenient way of choosing the right tag.
I really don't know how this works, but I do see the benefit of applying tag suggestions on travel.se
I would never came up with the tag "cell-phones", when I would ask a mobile phone question question. I would either use "gsm" or "mobile-telephone" as tag, leading to more anger for @hippietrail ;)
I honestly believe that having this tag suggestion would lead to less but more descriptive tags available.
I don't know what it takes.
EDIT Just noticed Stackoverflow uses tag suggestion as well. I made a screen dump. Notice that I did not use the word "svn" in my text, yet for some reason I am getting that suggestion, suggesting that there it is more to it then using words in the OP: