Tidal evolution of Earth-Moon systems

A dynamical study on the habitability of terrestrial exoplanets I: Tidally evolved planet-satellite pairs
http://arxiv.org/abs/1210.1640

Evolution of systems similar to the Earth and Moon over 4.5 Gyr. Three possible outcomes are found:

1. Still evolving towards synchronisation (similar to Earth-Moon)
2. Double synchronous (similar to Pluto-Charon)
3. Satellite collides with the planet

They estimate roughly 2% occurrence of Earth-Moon systems similar to our own that are still evolving towards double-synchronisation after 4.5 Gyr. The vast majority of double-synchronous systems have long rotation periods (>96 hours) that may be detrimental to habitability, and may have less efficient ocean mixing.