If you want more detail, I'm too lazy to explain, so you can visit the webpage detailing the process here. Basically it gives you recognition within the community, and entitles you to an @ubuntu.com email address amongst other things.

I've already signed the Ubuntu Codes of Conduct (CoC), so I figured I may as well try for membership. I figured I'll try the next time it comes up (the next EU meeting is tomorrow, and I wouldn't be able to make it). They require you to have a wiki-page as well, so I've even had to delve into the wicked world of wiki-editing