I think a manual tag system would require a lot of investment, either technologically and socially.
Solutions around automatic text qualification might be more efficient ( like a "similar questions" nodelet) and easier to implement.
See also term frequency–inverse document frequency for a possible approach.
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery
FootballPerl is like chess, only without the dice
PS: not sure why this was down voted, probably one of my fan boys.
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