It’s not just people who ask questions on the site that benefit from the experience of the answerers: several packages now “out in the wild” on CTAN started life as answers to questions on TeX.SX.
In fact, way back before TeX.SX even existed (imagine that!) over on stackoverflow, Konrad Rudolph created the minted package in response to a question about syntax highlighting. There are now 23 questions tagged `minted` on TeX.sx. I don’t know how good a measure of package usage that is, but it’s probably a pretty good indicator that this is now a much-used package.
Martin Scharrer has a habit of spontaneously writing small packages in response to interesting questions. In response to dealing with whitespace in listings, Martin threw together `lstautogobble`. And, another listings related small package: `lstlinebgrd`. This one allows you to colour the background of lines of a listings environment. Neither of these packages are on CTAN (yet) because they don’t have any documentation written up.
After having worked out a hacky answer to a question about beamer colour themes, I spent a while throwing together `colourchange`. (Note the British English “u”). This was my first attempt at a package and I learned a lot from doing it. I’m planning to go back and rewrite parts of the package to make it more readable, now that I know a little more about how best to do these things.
I took up the challenge that Martin threw down in a question about adding input line numbers to drafts, and started writing `draftinputlines`. I’ve just noticed that the mysteriously named “You” has done a similar thing here.
I think going further than just answering the question as it is asked is a great way to learn a lot about TeX and friends. I think I get more out of answering questions than I do out of asking them. (And not just because upvotes to answers are worth twice as much as upvotes to questions!)
In fact, there are several package maintainers that are regular contributors to TeX.SX as well. I’m sure some bugs in `siunitx` have come to light in questions on the site, and Joseph Wright (`siunitx` maintainer and TeX.SX moderator) has been quick to release fixes. So the TeX.sx site hasn’t just helped those people asking questions here, we’ve also added useful packages that everybody can use!
And finally, there is, of course, the TeX.SX TikZ package currently being produced. We have some mighty TikZ magicians on TeX.SX, and Andrew Stacey had the excellent idea of turning some of their great work into a package. I think they had hoped to have a release candidate in time for the birthday last week… Let’s hope this extra publicity prods them into action!
Please let me know of any other instances of packages inspired by TeX.SX in the comments.