AutoPager automatically loads next pages when you reach the end of a page. It works on a ton of sites,Google,Yahoo..
It works well with most other add-ons adblock plus, WOT and most of the greasemonkey scripts
It works with MetPage too. Nice to read through threads by just scrolling up and down through the pages.
Yeah, it's a nice feature to have when you're reading a thread with many pages. No more need to keep hitting "next page". Not that that takes a lot of time or effort. Just nice not having to do it.