Movable Type 4 is out and going for the “social media sites” angle.
Having worked extensively with version 3 at The Age it’s very different to WPMU in a whole heap of ways… and I reckon it’s time for someone with less – ahem – bias than me to do a decent side-by-side (possibly chucking in Drupal and Elgg for god measure?)
Any other software that really ought to feature?