In October of 2011 at the Do It With Drupal Conference, I talked about Upgrading from Drupal 6 to 7
Drupal 7 has a lot of really nice new features in it, so upgrading your site could bring a lot of benefits. Upgrading can look straightforward in writing but there are a lot of little things to pay attention to in the process. In this session we demonstrated the steps of upgrading a site from Drupal 6 to 7. We looked at Drupal core with some contributed modules as well, including making sure that things like our old CCK fields and Views get updated properly. We then talked about the resources available if you need to update any custom modules or themes as well.
I also created a Fantasy Site, Groupal, an example of trying to re-create Meetup.com in Drupal. I incorporated Organic Groups with events, locations, rsvps, photo galleries, and activity streams, all stitched together with Panels and Views. In the process of building this out I had to analyze which of several alternative modules to use for location, signup, activity stream, photo gallery and other functionality.