Why would one need Software Collections?

Evolution is one of the worst for this. On their mailing list they often answer upgrade questions with the answer "Oh, you have to install Evolution 3.0, let it update your files, then run 3.4 or it won't work."

Well, to do that you have to build all of Evolution, from source, and hope really hard that one of the libraries it wants to link didn't get upgraded to an incompatible version in the meantime. If it did, you have to build ALL OF GNOME 3.0 from source, in its own installation directory, then build Evolution. Or, find each incompatible library and build an older version, then point the configure script to the older version, by hand, for each library.

You might, possibly, be able to point a Fedora 18 yum at a Fedora 14 repo and hope it worked. Or maybe try an install into a chroot. Or a minimal install into a virtual machine.

Software authors really need to *think* about these things when updating data formats. For example, if Evolution used stand alone programs or scripts with no external dependencies for upgrades, the entire upgrade series could be installed with the package. Then you could run 2.20 to 2.24, 2.24 to 3.0, 3.0 to 3.4.