From a user standpoint, OpenID has little to offer to me usually. Most sites have a simple enough registration (email and password) that it really isn't that much easier to use openid in its place. To add to the confusion, Google and Yahoo have long identifiers, and you must use a seperate button to login with them.

From a website owner standpoint, it's so hard to implement, both technically and conceptually (tying into my sites regular registration flow) that it just convolutes the process for the user.

For example, as far as I know since the last time I attempted implementing openID, the only info I am guaranteed to receive from an openID identified user is their identifier. So if my site collects email addresses or any other info, I would have to have them enter that anyways.

In most cases OpenID registration actually takes longer, just so the user can use one account password.