I first noticed this when looking at the trends on Twitter and saw #InstagramStories. It took me a second to figure out how to post a story on Instagram, but it's the plus sign button in the top left corner of the screen. Just like Snapchat, you can see who's looked at your story.
I'll be interested to see how many of my friends start posting stories to Instagram. I'm not going to make public predictions on what I think will happen after this, but I will be interested to see if Snapchat responds to this. It'll also be interesting to see if this affects Snapchats IPO (initial public offering), whenever that happens.