This userscript gives you a convenient way of plotting a 0.1 mile circle around a cache on the Geocaching.com maps page. This is the minimum spacing allowed between the physical parts of different geocaches.
Once installed, it will add an icon and link to the popup that appears when you click on a geocache. When you click the link, the script fetches the coordinates for the cache, and plots a circle on the map at those coordinates. If you have recorded corrected coordinates for the cache, it will plot the circle at those coordinates rather than the original ones.
Updated 25 Dec 17 for compatibility with Greasemonkey v4 and onwards. Currently Tampermonkey or Violentmonkey is recommended as a Userscript manager, as Greasemonkey v4.1 doesn't auto-update scripts.
If you are new to userscripts, there is a HOWTO with instructions on how to get started.