Ahoy landlubbers! For this thing, I tried the Puzzle Pirates site. I did some interacting with other players (mostly other greenies - or new members) and tried 4 of the different skill games (carpentry, sailing, bilging, and swordfighting). I found that most other players were quite willing to chat or test their sword skills; however, in all cases, I had to initiate the conversation. The puzzles themselves were something of a disappointment ... they all seemed to be simplified variants of tetris/poppit puzzles. I found it especially hard while bilging not to be able to swap pieces upwards as well as across.
I also walked through the helps/faq on the Second Life site, but I chose not to sign up for an account. I hadn't heard of either of these 2 online sites before I started working on the 23 things. However, Runescape is very popular with tween age boys in our library, and I'm aware that WoW (World of Warcraft) is heavily played by some of the young adults (late teens and early 20s) that I know.
I am fine with patrons (of all ages) using library computers for online gaming as long as they abide by our rules (the primary problem we run into here is players respecting the time limitations when other people are waiting).