http://www.maven.co.il/whatsnew.asp Maven, The Jewish World portal directory

http://www.arthurschwartz.com/ The Food Maven (obviously not a woman)

http://www.jewishmaven.com/jewishmaven/ Phil the Jewish Maven (another guy)

http://www.bergen.org/AAST/Projects/Yiddish/English/comwor.html Common Yiddish Words (defines meyvin as connoisseur)

Connoisseur (male or female) is the main Yiddish meaning, but if people have made it a disparaging term, that may be a later development. Some people just don't like a know-it-all.