Upgrading Prattcenter.net from Drupal 6 to Drupal 7

The Pratt Center for Community Development in New York City is one of DTEK's oldest and best clients, and has been running on Drupal 6 for two and a half years (Andy migrated them from a custom php site in 2009). This will be a pretty tech-heavy post about how we planned and executed the major upgrade of their site from Drupal 6 to Drupal 7. The major question in any Drupal upgrade is whether to follow the core "upgrade" path - as defined in UPGRADE.txt - or to re-build from scratch and then do a data migration.