There are many other good reasons for a service like Github, like the excellent collaboration features, the really good repository and history browser or the good bugtracker.
If you don't need those (small team, working alone) but are concerned about uploading your intellectual property to a third party server in a potentially foreign country (depending on your location), then quickly setting up gitosis / gitweb / redmine might be enough for you.
In my personal case, I would really love to use github even for my small team, but I'm too concerned about the legal issues to go ahead with that (and the local installation is plain too expensive).
I can't imagine that GitHub would steal your code. They've never heard of you, they have no reason to believe your code is worth anything to them, and one "I have pretty damn good evidence that GitHub stole my code" could ruin their entire business.
You mentioned legal issues. Are you afraid someone's going to ... subpoena your code or something? Because if that happens, you'd have to turn it over anyway.
They've got some pretty intense-looking security, and people like Twitter trust them with their code. If they aren't worried, why are you?
2: I don't know that that's officially known, but I saw Twitter commenting on the "GitHub now has Organizations" post complaining about the lack of the cheaper plan that they added the next day. So they definitely have some private repos on GitHub.
Of course, I could always trust them for now and instantly remove my stuff when there are signs of trouble, but I asked them (a year ago) whether deletions are instant and irreversible and they told me the usual thing: repositories are not instantly deleted so they could restore them in case of accidental deletions. In addition they stay around in backups for an indefinite time.
Legislation not known well enough and no control over the removal of my code from their machines - call me paranoid, but these are good reasons not to upload my code to them.
Not if you don't live in the US.
Might sound unlikely but it happens.
Also, if github is down or your repo with them is corrupted, you have to go through their support. If your own server has a problem you can fix it instantly.
I'm not convinced that reliability is the correct reason to go GitHub. Features: Yes. Reliability: Not necessarily.
Data safety is all about fighting correlation. You don't back up one partition to another on the same spindle, because when the drive dies the whole spindle is lost. Paranoid people back up to two different drives, two different disk controllers, two different machines, two different datacenters, two different continents...
 But nonzero. It is worth thinking about the scenarios.
In addition to the remote repos on Github and my normal local copies...