There is an easy possibility to share caches between users of c:geo if both devices support near field communication(NFC):

Make sure NFC is enabled on both devices. Then just open the cache details of a cache on one device and place it back to back with the second device. This will automatically start c:geo and show the same cache on the second device. Even if c:geo is not installed on the second device, it will open the cache page in a web browser.