The Pebble appstore includes six categories and the best apps for each one will be curated to the top, making it easier for Pebble users to find them. The watch is limited to the installation of eight apps at a time. In order to make switching apps easier, the 'Pebble Locker' is included with the update. This allows you to store those apps that you have downloaded but have not installed, and quickly swap them for an app currently installed on the watch. One app at a time can be exchanged in this fashion.
Those Pebble owners with the Android flavored variant of the watch will get the appstore update "very, very soon," according to Pebble.