Research Assistant
 

This is a very popular addon that causes some pretty serious performance issues. It causes small hitches when doing various things, like every time a melee swing lands, or you loot a container. It's easiest to tell while meleeing - try it with the addon turned on and off, and you'll see a freeze for a frame or two. It took me a really long time to pinpoint what was causing the issue, and if you check the comment section you'll see more of the same. I think it may be a good idea to at least put a warning on the addon page.