Yesterday, I was called an UberNerd by my GM. I didn't really deserve the title - I owe it all to Multishot.
A few of us had been chatting the previous night about dinging 80 through exploration - something I managed to do on Leesah. So, I posted Leesah's exploration ding screenshot, as well as Aefa's (coz I like it), on the guild forum. Having these screenies in the first place was enough to be called a nerd, but when I revealed that I use an addon to automatically take screenshots of achievements, well then the (affectionate) name-calling really started.
Multishot
Multishot takes automatic screen captures of events in the game. You can set it to capture your level ups, achievements, reputation level changes, boss kills (5-man or raid bosses) and rare kills.
The options are very simple, and the default timings work just fine in my experience. The captured screenshots can be found with the rest of your screenshots in your ".../World of Warcraft/Screenshots" folder.
The boss kills shots tend to be kind of boring - you have 2 seconds after the boss dies to get your screen in some kind of decent frame for a picture. I was mostly ending up with lots of shots of farmed bosses before I turned this option off - I just don't think it's worth it.
The entry on wowinterface describes Multishot as "...a photo diary of everything you come across in Azeroth, Outland and Northend." That's pretty much the reason I use it. I like to take pictures to remind me of things, and it's nice to have a record of where you got certain achievements.
Not to mention that the achievement captures can make great blogging fodder!