I have problems with OpenID, too, because I tend to be unable to remember which OpenID login I used for a site.
Or maybe it was that Yahoo creates several OpenID logins?
Google turns up a Quora thing which, frankly, is full of handwaving bullshit.
Are there actual technical reasons why OpenID is bad?
And the reasons are mostly ones of user-friendliness (not technical reasons). I've heard of plenty of people who still never signed up for StackOverflow because it requires OpenID.
The abstract idea was good, the standard itself is awful.
You need look no further than any of the stackoverflow related sites to see a very successful large scale site using OpenID.
I'd also suggest looking at tripit.com, catch.com, mindmeister.com or springnote.com to see excellent examples of OpenID login done in a way that's very user friendly while also providing the option of a traditional login for people who prefer it.