I've also used GSAK for a few years. Initially got it to support formatting of pocket queries so they could be loaded as POI's on a Garmin Nuvi. We are able to setup proximity alerts for gc's based on how close they are (current set to 1500 feet). This has become something we can't live without. Currently using this on 2 Nuvi's for both vehicles. If we are within 1500 feet of a cache, we get an alert from the GPS, with a small window pop-up. We can click the pop-up and read the cache details (description, logs and hint if needed). This makes for some great unplanned caching, especially if we are in an area away from home.
Initially we had simple PQ's loaded for various locations around the state, but this past year we figured out how to get the entire state of NJ loaded on the Nuvis using a series of 14 PQs (using date placed filters). I loaded all PQ's into GSAK and generate a single gpx file formatted for the garmin. Currently there are close to 12k. Thankfully both Nuvis can handle that many POI's.
Also use GSAK to track stats and update gc.com profile page for more than 20 statistics including FTF's, finds by state, county, country, etc.
It's a great tool that I don't think we could live without.