Having personally signed up several people a week for the last couple of months - nearly all of whom are quite happy with where the site is at - I have found what works the best (for content producers) goes something like:

"Hey, you want to see my latest art/essay/(fill in the blank)?"
"Sure! Where can I find it?"
"Have you heard of Steemit? I'm putting all my stuff there these days!"
"No ... Steemit? What's that?"
"It's where all the best creative people are starting to put their stuff. They actually pay people for adding value to the site."
-Long Pause-
"I'm making an extra hundred bucks a month using it. It's not much, but it's not nothing, either."
"Really?"
"Yup. Check it out. I'm Hive account@mada. The site's still in BETA, so it can get kinda tricky. If you sigh up, let me know, and I'll walk you through how to do it."

Steemit's perceived stability needs a bit of work before I will feel comfortable mentioning the site to my serious investor friends. But signing up new users who come in with realistic expectations and stick around is super easy if you keep your pitch simple and honest.