Way back when, we had a discussion with da Flier about learning how to maximize our Nuvi memory with an SD card. We never did figure that out, HOWEVER while trying to figure that out we discovered This website, and subsequently downloaded the POI loader and the macro for GSAK--we were able to load 4900 caches as POIs into our Nuvi and IT DIDN'T CRASH!! It is awesome. It no longer shows the caches as giant treasure boxes on the maps as it did when they were in the favorites menu, but instead as tiny green markers. You can set it to alert you if you get within a specified distance from these caches, or you can have it remain silent. It loads all of the cache info, including the hint and logs, into the Nuvi as well. We are thoroughly impressed and wanted to share the knowledge. We still haven't figured out how to make it put that info on the SD card, but I'm sure with more reading on that site we will figure it out.
Here are the basic steps:
Download the POI loader.
Download the Nuvi Macro and add it to GSAK.
Run the Macro in GSAK--it will have some onscreen instructions for customizing the POIs.
POI Loader should open automatically--follow the on-screen directions to load the POI files to your Nuvi.
Voila!
I hope this helps at least one person--I was pretty thrilled when we figured it out!

Edit: It helps to include the link. It's there now!

Recently back from a multi day cache run in the S.W. and one in the group had a Nuvi set up in this manner.

MEGA IMPRESSED says Da Flier.