Just a small accomplishment, yet I'm very happy. In the last days I was having a lot of 404 reports for a no-longer existing page on SkakkiNostri. The referrer page was null, so I had to find the source myself. I grep'd the source code, queried nearly every table in the database, but there was no link to that page there. So chances were a) some search engine b) some user.
Looking at the UserAgent/IP address, I quickly found it wasn't a search engine. So probably it had a user that dumbily had bookmarked that page, and now used my 404 error page to come back to the site. I have been thinking about what I could do to avoid this error, then I had a sudden realization: I could just track down the user using the cookies collection and send him a private message. Guess what? It worked. The user wasn't understanding what a 404 error was, but could access the site, so he was happy. Nonetheless explaining the situation to him we have been to fix the wrong link in the Favorites, and I'm no longer receiving emails. Well, not for that error :)