JISC has released Ensuring That 'E' Doesn't Mean Ephemeral: A Practical Guide to E-Journal Archiving Solutions, which discusses CLOCKSS, Portico, and the UK LOCKSS Alliance.
Here's an excerpt:
This booklet provides a starting point for institutions interested in investigating e-archiving options. It gives a practical guide to the solutions offered by three of the main long-term preservation schemes and provides an overview of the distinguishing features of each solution.