jdsgn: So, if I do not want absolutely everyone to be able to see and copy my repository, I have to pay?
For private repos, you have to pay, though like elendiel suggested, their lower-tier fees are quire affordable.
Alternatively, you can always stick a non-commercial creative commons license to prevent others from using your code for commercial purposes.
While it's based on honor, bigger private companies wanting to use your code for commercial purposes (extremely unlikely occurrence btw) will want to make a deal with you rather than potentially tarnishing their reputation and exposing themselves to a lawsuit.
elendiel7: There are several tiers available on their website with a monthly fee. I personally like releasing Free Software, so I'm perfectly content with free repo's. However, the only people that are aware of code I upload, are the people I explicitly tell. Normally newer repo's or ones that you don't advertise to exist, usually don't have many, if any, prying eyes.
Usually, I'll see a clone or two in the first couple of days after a project is out (happened with practically all my projects so far), probably from people who are curious to look at the code rather than seriously intending to use it. But yes, people tend to have an overinflated opinion of how desirable their code will be on Github.
They are worried about others profiting from their code while leaving them out of the loop, but more often then not, others are not that interested in their code and whatever they end up putting on Github will have 2 main uses in the grand scheme of things: a glorified personal backup and something that looks good on their resume.
I must say though, some channels do provide more visibility than others. My node.js specific code has had far more visibility on npmjs. When I update some projects there, I'll often see a couple hundreds of downloads after the update. I'm guessing someone in that mass is actually using it.