I was at Chabad this Shavuot and they did not read Ruth. Everywhere else I've been (all Nusach Ashkenaz) has read it claiming that it's appropriate since this is the time of the wheat harvest.
Are there other groups who do not read Ruth on Shavuot? Are Ashkenazim the only ones who do? Where did the custom originate?
Also (and maybe this should be a separate question), does Chabad (and other groups who omit Ruth) read Kohelet on Sukkot?