Github doesn't have their own share buttons believe it or not. Everyone uses these by @mdo (the Bootstrap guy) and they've become the defacto standard. They are modeled after the native twitter buttons so at least you get some visual consistency. It's a bummer they use iframes but only Github could do better with an official integration.

I typically host them locally for a few reasons:
* One less DNS lookup in the call stack for users
* The default buttons have a blue hover state that clashes with your teal. I edited the local CSS to match the white/gray gradient bg and border-color hover state of the twitter buttons
* I typically run my sites over SSL (which requires hosting locally cuz @mdo's CDN doesn't support it) doesn't apply here today but eventually you'll want to