From Meta Stack Exchange:

Accounts which are deemed to be abandoned will be deleted, and the user information on their questions and answers will be denormalized into text fields.

Cookie-based unregistered accounts will be deleted when:

1. The user has not visited the site in six months

   AND

2. The user has less than 50 reputation.

OpenID registered accounts will be deleted when:

1. The user has not visited the site in six months

AND

2. The user has only 1 reputation (i.e. has never received an upvote)

From Meta Stack Exchange:

Accounts which are deemed to be abandoned will be deleted, and the user information on their questions and answers will be denormalized into text fields.

Cookie-based unregistered accounts will be deleted when:

1. The user has not visited the site in six months

   AND

2. The user has less than 50 reputation.

OpenID registered accounts will be deleted when:

1. The user has not visited the site in six months

AND

2. The user has only 1 reputation (i.e. has never received an upvote)