Question: I'm running F17 and inside of `yum.repos.d`. I see multiple repos listed like `adobe-linux-1386.repo`, `fedora.repo`, `google-chrome.repo`, etc. When I `yum install` are some files being downloaded from multiple different repos or all from one?

Answer: 
Most of the repositories specify a `mirrorlist` in their configuration file. When present, `yum` will select one or more of the mirrors provided by the list. Repos that don't have mirrors will have `baseurl` instead of `mirrorlist`.

When downloading multiple packages, yum can download from multiple sites in parallel, though this isn't always obvious in the terminal unless you watch very carefully.
Normally the contents of repository do not have the same rpms (like in your example). If you had "conflicting" rpms you can use yum\_priorities to choose which one to use first.

But in the end a single rpm will be downloaded from a single (mirror)-server that is mentioned in a single repository (directly or via mirror-list).