Yahoo’s decision to become an OpenID provider is a one-way street, and will serve mainly to enhance Yahoo’s knowledge of its members’ browsing habits away from Yahoo’s many properties.

While Yahoo’s OpenID implementation will add its 250 million registered usernames to the pool of OpenID users, greatly boosting the credibility of the data portability movement.

But the true openness will occur when Yahoo itself accepts OpenID logons authenticated by other OpenID providers, like MyOpenId.com, an independent OpenID provider operated by OpenID heavyweight JanRain.