New Excel Services MSDN Forum!
MSDN has created a forum for Excel Services related discussion, you can find it at: https://forums.microsoft.com/MSDN/ShowForum.aspx?ForumID=1208&SiteID=1
We're working on a more readable shortcut, and it's empty as of right now but you can expect the content to grow and there will be folks directly related to Excel Services development involved in answering questions.
Enjoy!