Google has been sending out announcements reminding all customers that appear to still be using the Email List Provisioning API that the API will be de-commissioned on 8/31/13 and that applications that use it should be updated to use the new Directory API.
My application only uses the email list API indirectly, in that the User Provisioning API will return a feedLink element on User entries that points to the emailList API for a list of email lists/groups of which the User is a member.
I'm wondering if that feedLink will a) go away; b) remain but be broken since the API it points to is gone; c) remain and actually work transparently; d) be replaced by a different feedlink; e) some other option that I haven't thought of.
This is important because using new Directory API is a massive change and yet doesn't seem to provide a simple documented way of retrieving the group memberships for a single user anyway.
Last things first, you can determine the memberships of a given user with the Admin SDK by using the groups.list() call and specifying the user with the userKey attribute. This will return only groups the user belongs to.
I am not certain what the feedLink will do but it seems reasonable that it will either a) go away or b) remain but be broken.
You should definitely not count on it's continued use.