Fashion is a relative newcomer to the reputable Metropolitan, but now the Upper East Side institution is stepping into the fracas of the fashion blogosphere. The museum is displaying 40 new acquisitions from its Costume Institute in blog.mode: addressing fashion, and — hold onto your chapeau — inviting the public to comment on the pieces through a blog on its website. While the armchair fug-sters do battle for most catty remark, the Met's sincere curators intersperse relevant art-historical commentary about such highlights as a 1983 black Comme des Garçons jersey dress and a 1947 Adrian piece featuring a Salvador Dalí design. While the high-class items are undoubtedly worthy of the Met's collection, it's the public dialogue that merits close scrutiny.