My guild leader mentioned that he spent a lot of time on our guild’s leaderboards page searching for inactive members to boot.
Since the achievements API has not been released yet, I published a Chrome extension to make it very easy to see who is active on the leaderboards.
You can find the published extension here:
https://chrome.google.com/webstore/detail/guild-wars-2-achievement/ilclbnmllchoomhpikjodcpaccaglokc
I also uploaded the source code to GitHub:
https://github.com/FoolMeOnce/gw2-activity
Feel free to contribute code, use the source to create a Firefox version, or even use it to as a starting point to make your own extension!