To add to Steve Vickers' remarks: Category theory is definitely out of the closet. A substantial number of the questions on MathOverflow involve categorical concepts and many of them are questions about category theory itself, not merely applications. The n-category café blog and its ancillary n-labs has lots of category stuff, both applications to physics and about category theory itself. Charles Wells -- professional website: http://www.cwru.edu/artsci/math/wells/home.html blog: http://sixwingedseraph.wordpress.com/ abstract math website: http://www.abstractmath.org/MM//MMIntro.htm astounding math stories: http://www.abstractmath.org/MM//MMAstoundingMath.htm personal website: http://www.abstractmath.org/Personal/index.html sixwingedseraph.facebook.com [For admin and other information see: http://www.mta.ca/~cat-dist/ ]