All admin are encouraged to read recent changes to Help:Blocking to understand a subtle point about proper un-blocking procedures. When unblocking someone, it's important to remember to unblock their IP address as well, or else they'll appear to be unblocked, but they still won't be able to edit.

Thanks to Cyruptsaram and OttselSpy25 — as well as Ciencia Al Poder, Rappy and the rest of the gang from the Wikia IRC channel — for pointing out this odd behavior of the blocking feature, and getting us on the road to establishing a better unblocking procedure.
czechout ☎ ✍ 20:51: Tue 17 Jul 2012 

Furthermore, a new guide has been written to help users who have gotten blocked to understand what their options are. It's at the easily-remembered Help:I'm blocked.
czechout ☎ ✍ 03:55: Wed 18 Jul 2012