I thought that it was more a matter of time rather than quantity of hubs. *Remember, you want to go for quality over quantity (if you have to pick one); and you want to write about what's called "evergreen" topics -- not flash-in-the-pan, issue of the moment things. You want to write about things that people can constantly learn from.
Most of the people I've heard from on this issue have said that it takes about a year before they got their first check. I've been with HubPages going on ten months now and I've yet to receive my first pay out.
Remember, there are billions of people on the Internet and it takes time for one to be discovered by a "mass audience" (if that is what you want) -- there's lots and lots and lots of junk on cyberspace to wade through, and that takes some time.