Pocket used to be Read it Later, a paid app. Early this year they switched to Pocket, went free, and raised $5m. So right now, afaik, they don't make any money.

The founder has said in articles/interviews that going free was the right choice for pocket, they're not looking to be acquired, and not ready to talk about their future business model/revenue streams, heres him from July when asked about their plan:

We’ve known where we are headed since last year. But like anything we do with any product or feature, we don’t release it until it’s ready. This is a new, uncharted space and we’re not prepared to release something that isn’t right.

I'll admit, I'm pretty weary of the whole thing, but willing to see where it's headed, I guess. I think if their plan was to just flog off their users data, they would have started doing it already, but it seems like they have something else (Hopefully interesting/unique) planned.