There's some of both in the open-source world. You do have a lot of personal-interest projects out there, but you've also got a lot of projects run by companies that hire developers to contribute (i.e. Mozilla, all the work Novell does on Mono, etc.
The line between the two can also be a bit blurry, too: in OSS, there's nothing stopping a company like Canonical from contributing to a personal-interest project if they have something to add (like patches, whatever), and there's nothing stopping an individual from contributing to one of the huge corporate-run projects like Mozilla (I could find a bug in Firefox that interests me, submit a patch, and if my code were up to snuff, it would be in the next Firefox release).