There are a lot of issues with OpenID. Meta has a lot of questions related to problematic logon using OpenID and the Internet is pretty much full of horror stories related to OpenID. I've personally been hit a lot of times by problematic OpenID login to stackoverflow.com using Yahoo OpenID1.
Now I'm wondering: at which percentage of users encountering issues would you consider providing the usual site-specific email (and/or login) + password? 0.001% of users having problems? 0.1%? 1%? 10%? 50%? 99%?
I'm clearly asking about using something else than OpenID, because to me this:
is just begging for more OpenID issues (at least being your own issuer I can see how it could help have less problems, but it still doesn't seem like a stellar idea).
That "Help us test and vet StackID" is a clear sign that OpenID is problematic: in that case it is explained that MyOpenID is repeatedly having issues. So MyOpenID is repeatedly having issues. Yahoo! too. Others probably too.
For example there's this question and the answer tells you to "write down the ID and contact us":
Some of the issues are so common that there's a "procedure" (a manual procedure, how is that even possible?) allowing for people to merge accounts.
So it's really an honest question. What's the percentage of users that need to have issues before you'd consider using something else than (and in addition to) OpenID?
For example should one day, say, Google or Yahoo! mess up royally their OpenID and should you have a gigantic number of users kept out of your sites, you'd have to do something right? And I can't imagine all these users having to cut/paste their ID and trigger your manual "account merging" procedure.
1Just FYI: today I can't log in using Yahoo! because everytime I'm sent from SO to the usual Yahoo! OpenID "J'accepte" (French email at Yahoo fr) I get redirected to the same Yahoo! page... but in English! And then clicking on "I agree" simply constantly redirects me to "I agree". I tried on several OSes and several browsers. No luck. And that's one time too many: I've got 6.5K rep on SO but this time I'm gone for good.