Here's my longest running account with no funding changes from December 2013 to today:
http://seaofbtc.com/harrisonkinsley/honeybadger/client/1 It will take a while to load. That's done by automated day trading, and it's done using a mindless grid-strategy that anyone could do by hand, it's not high frequency. I just choose to automate it so I don't have to sit there all day and don't miss any trades. Bitcoin is volatile, so it works, and I've significantly beat the market, but there are plenty of totally possible events that could leave me far behind market performance never to recover again.
It's hard to know if your profits are a result of alpha or beta. Measured in BTC you are clearly ahead, but then you've probably been at least partly in USD a lot of the time. The market has been in a more or less continuous decline, so you would have archived about the same result by just staying 50/50 in BTC/USD. Unless the bitcoin price goes back up and you're still ahead you can't really know if your model beats the market in general or just the current market conditions.