Evolution’s default IMAP provider does not support shared folders. The problem is of course in the code that handles namespaces. I fixed this in Tinymail‘s camel-lite. I know this is a much requested feature for Evolution too.
I would like to point out to the heroes who’ll, in stead of begging for me to port the patch to Evolution, this time port the patch themselves, that the patch is a.t.m. in a very ugly state (I made a few shortcuts in the code). That camel-lite’s LIST code for IMAP has been adapted in multiple places to consume less round trips (it might not apply easily on upstream Camel, you’ll have to do quite a lot of merging). That this stuff is experimental and that a raw port of the patch would most likely not get accepted upstream yet.
If you want to work on this perhaps join one of the IRC channels that I use and let’s discuss how we’ll clean it up and bring it upstream.
Edit: I’m making more intrusive changes for Tinymail’s version right now. Check Tinymail’s mailing list to follow up on this (for example this one).