Where did the Share Screen option go in Mountain Lion?

In recent previous versions of the mac OS, I used to be able to select a shared computer on the sidebar in a Finder window, then there was a button next to the connect... button that also said "Share screen" or similar. It is no longer there. Nor is there a similar command via the contextual menu or on the Finder menus.

So, how am I supposed to share a screen on another mac?