My reason for no: Security concern. Sites issuing OpenID verification have all kinds of security features and I don't want parts of Dreamwidth's security to depend on what other sites do.

This would allow me to use my OpenID for its (as I understand it) intended purpose: de-cluttering my mind of username/password combinations.

Well, that's not its purpose :) As cesy said, it was designed for cross-site authentication. Quite frankly, using the same very secure password is a better way to handle that problem. Even if it's also not ideal, at least it won't introduce a site-wide security risk.