From an interview with Leon Li of Huobi, at one point the biggest exchange of all. Dunno about today.
"As to the question “How many users trade on an average day?” It involves our website operating data and I cannot give the exact number to you. It is over ten thousand. And this number, compared to the vast population of China, is still very small. Therefore there should be more space to grow."
http://www.financemagnates.com/forex/analysis/exclusive-interview-ceo-of-largest-bitcoin-exchange-in-the-world-huobi-responds-to-mt-gox-situation/
Let's look at that figure again -
10,000
people were using the WORLD'S BIGGEST Bitcoin exchange every day.
Can you see room for upside still? If I try really, really hard I think I just about can.