RFC 1641 proposes the use of Unicode in MIME messages.
To avoid encoding large amounts of ASCII text in base64 when only a few ``true Unicode'' characters are used, RFC 1642 proposes an ``inline base-64'' encoding called UTF-7 (the HTMLized version at the Unicode Web Site is better legible). IMHO, UTF-7 sucks, but then I am no great fan of MIME's =xx encoding.
There is no newsgroup dedicated to Unicode (yet), most UNICODE-related discussion occurs in comp.std.internat.