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.
Most packages would be downloaded from fedora.repo. Adobe packages would be downloaded from adobe-linux-i386.repo. Google Chrome packages would be downloaded from google-chrome.repo