As I read it, 'metro switch' is equal parts marketing differentiator and technical features. On the tech side, it's generally support of features such as MPLS or POS that allow and Ethenet switch to integrate directly with a carrier's transport network without the need for protocol conversion - e.g. the Ethernet frames are moving intact (potentially encapsulated) through a carrier infrastructure.
This Q&A document may help somewhat: http://www.cisco.com/en/US/partner/netsol/ns577/netqa09186a008010597a.html
Hope this helps. Please rate helpful posts.
