Geocoding UK addresses has always seemed to be a pain especially outside of Drupal. With Drupal 7 a few of the mapping/location modules that I have been used to using in Drupal 6 are either not available as a stable release or don't quite do what I wanted. A key example is Location which I have used on a Drupal 6 with which geocoding has never worked (I still don't know if it is something that should work out the box, it certainly seems to imply to me.)

A rash of new Drupal 7 modules has made the process a lot easier though.