This is one of my favorite GC GreaseMonkey scripts. If you get the 'Show all logs' script it really makes this one shine (as this works by scanning the logs and that one opens them all up automatically).
It has many things it does but I really like how easy it is to quickly see if a friend has found a cache. You can also quickly jump through logs to see specific posts. If a cache has over 200 logs wading through it to find the three DNF logs can be tedious, this makes it easy. It has some nice customization options for placement of the VIP List, adding friends en-masse or just seeing if someone is on the list.