If you count the approximate value of credit card rewards (miles, points, etc.) then I earned ~11,000 extra last year. If you leave out credit card bonuses, then ~4,500 before expenses, taxes, etc. I do a bit of web development on the side, open checking accounts for the bonuses, and a few other things (I am nearly done writing a blog post that summarizes it all up).
I think 2016 is likely to be a bit lower, but thinking of and executing side hustle schemes is one of my hobbies, so who knows! I have an idea for a pretty simple ebook to try on Amazon, but I've been procrastinating actually writing anything for 6 months.