I upgraded this Orchard 1.6.1 website to Orchard 1.7 RC for practice to make sure 1) there weren't any surprises, 2) get ready for client upgrades, ands 3) test the Orchard CMS 1.7 upgrade to report any problems. The upgrade was simple and painless given I have done Orchard Website upgrades for the past 3 years and I continually keep my websites on the latest release of Orchard CMS. Despite the new Media Library and changes in Taxonomy Module, Output Cache Module, and Content Picker, upgrading my website to Orchard 1.7 was a breeze. Update: Orchard 1.7 was released!
The three most important changes handled by the Orchard 1.7 Upgrade Module since Orchard 1.6 are associated with the Content Picker, Taxonomy Module, and the new Media Library. Upgrading the Content Picker is a no-brainer and may not even do anything if you are not using the Content Picker in your Orchard Website. The Taxonomy Module now ships with Orchard as opposed to being a Contrib Project, so if you are using it in your current website you'll need to run that migration process. And last, if you are interested in using the new Media Library that ships with Orchard 1.7, you'll need to migrate all the images in the media folder into the new Media Library. As an observation, I like the Media Libary upgade process as it tells you how many images it needs to migrate and gives you a continuous count of the image files still needing to be processed.
You can learn more about what's new in Orchard 1.7 by reading my tutorials: