Legitimate mirrors and people who want to reuse our content are free, and encouraged, to download a database dump and process it for their needs.
Say, are there examples of people who do this well, contributing back to Wikipedia or to the general public? The examples I've seen are all a bit disappointing, but perhaps that's just because the outrageous ones generate more attention.
Yes, several sites do this quite well. See for example http://www.answers.com. --Mets501