Since I started leading a raid, I have been making spreadsheets to keep track of which players have which achievements towards the raid meta achievement ("Glory of the x") and I got tired of making them. I have spent the past few weeks learning PHP/MySQL and browsing these great forums for ideas, and the beta version of the site is finally ready.
I am gathering guild name, region, realm name, and toon name information from users, and then performing API queries on those toons. I store all of the data in MySQL, then I compare the known achievement values (like 6175 = Holding Hands) with the toon's JSON API data to figure out who has what achievements. The resultant info is then displayed in an easy-to-read chart and cached for further usage (and can be refreshed by the user).
The biggest problem with the site is the raw amount of work it takes to gather the icon images for each achievement, which is why only Dragon Soul has images and the other raid metas are text (for now). I already have all of the Pandaria raid meta info programmed in as well, in preparation for MoP's release.
Let me know if you have any questions on how anything is done, comments, or feedback (positive or negative). Thanks for looking!
P.S. - All of my guilds/groups are on Azgalor-US if you want to browse a guild without programming one in yourself.