I've always been fairly old-school internet in my thinking when it comes to monitization. "Build something cool, figure out how to make money later."
JustSketchMe up until now has been running on user contributions, usually totalling about $300 per month. That's not much considering the number of users (35k per month now).
I've updated the webapp to have all new features paid. All the old features remain free, but new ones like saving and loading poses are now $5 per month. I launched this new model yesterday and already have 3 paying customers...and that's just for one beta feature!
Let's see how things pick up as I start adding more premium features!