Epic recently updated their UE4 SteamVR plug-in code and made these changes public.  While it is not possible to use these changes just yet, they provide an interesting view into what to expect from the HTC Vive.  I went through the source code and picked out some interesting items, and posted my results on reddit here:

http://www.reddit.com/r/oculus/comments/323cpg/ue4_now_has_updated_steamvr_support_provides/