Quite a few people have complained they can’t easily find the share button on Google+. Here’s the UI:
The problem is that the Share button is below that Friends button. Friends isn’t really a button, more like a tag, but it looks like a button, and that’s what matters. Your eye is in the textbox (you’re typing), and the friends/more people crap stops your eye from looking below that for a Share button.
Easy enough to fix though.
Make the Share button more prominent (visually) than the friends button. And move it to a central place right underneath the text box. Oh, and don’t grey it out.
Something like this: