Right now only about $300 a month but it is fairly passive. I also do freelance work and sell other products.
I recently started using Google AdWords as so far I've done very little marketing. Hopefully AdWords can improve that number into something far more impressive.
I'm also building a couple of other websites which I think have potential to make a lot of money but they will take a while longer yet.
It's my ultimate goal to build a sustainable living from software products online. I think it's a realistic, yet very difficult goal but I'm enjoying the challenge!