Good point, it was full of spam and registration was closed. I forgot about that. It was because we had a really old MediaWiki version so it was actually unsafe to allow anyone untrusted to post on it due to exploits possible at the time. I say “we”, I don't have access to manage haskell.org. I'mma ping the mailing list to see about fixing this.
I think that's an excellent idea. Well-done.
If the Haskell Wiki didn't require me to e-mail somebody personally and ask for permission to register, I'd be much more inclined to provide a one-of edit. By the time this person gets back to me (he's probably in Europe), I'll have neither the time nor inclination to make a one-time edit to a wiki that I've only visited on a handful of occasions.
I gnome-edit wikis all the time -- at least the ones with user-friendly sign-ups. Was the Haskell Wiki so beset by viagra spammers that it had to institute a human-mediated registration process? Maybe it was, but the downside is that then people like me are less likely to register for one-off edits.