"To me it does matter. If it's not secure, somebody could easily log in as moritz, and with a few writeups could destroy the reputation (and perhaps even trust) that I built by writing more than 2000 posts."

Right, I see why having your account broken into is something that bothers you (and me), but that could happen in any other form as well (again: Yahoo! Palin. Mail). First of all, the "attacker" has to guess which provider you used (obscurity, yes never good). In this case, Perlmonks would be an easy guess.

Secondly, the "attacker" needed to somehow authenticate at Perlmonks with your credentials. So, rather than fearing OpenID being insecure, you really shouldn't trust Perlmonks security. So here it boils down to what OpenID provider you trust.

I haven't seen stories where OpenID was spoofed (if you have stories, please let me know). I can only think of DNS attacks (?).