I agree entirely with Eliah Kagan's answer.
In addition I would like to point out that the importance of correct tagging is underlined by a nifty privilege you get at 10k reputation.
###Inline tag editing
Finally, you now have the ability to do inline tag edits on questions. Hover your mouse next to the tags and you should see a "edit tags" button
Since questions are often tagged wrongly, I often use this tool to edit only tags. Questions with irrelevant tags, or lacking relevant ones, are less likely to be seen by the many experienced users who follow particular tags and are likely to answer questions in their area. So, a tag-only edit can be very useful.