I've never made software professionally, but I imagine the curve of getting used to a new company's systems would eat up most of that time, making it more of a hassle than it's worth.

If there is a way to overcome that though, this sounds like a cool idea.

This is what I love about consulting - I can experience different team cultures and projects, and learn what works and doesn't work for various teams.

Well, as a front-end developer I'm pretty comfortable using a lot of technology (Ruby to .NET)

My proposal is to really have companies to align their resources for shared knowledge. I think the managers would have to be the one to make the call about what information is being accessed by that said employee.

The "learning curve + getting up to pace" cost might beat the pros. And like alloftheabove mentioned, company secrets will definitely be a issue with the larger companies.

This would be cool. biggest hurdle would probably be employees taking company secrets with them, so maybe it would work better with only open source development

Check out grouptalent.com. It might be what you are looking for.

So... internships?