Michael Valentine Jones (1/22/2013)
Generally speaking, you will not see much improvement from having multiple tempdb files, except under specific conditions that are fairly rare.
This is good info, but slightly old. The current recommendation from Bob Ward, of MS and CSS, is one file per core for < 8 cores. Above that, use 8 files and monitor: http://social.msdn.microsoft.com/Forums/br/sqldatabaseengine/thread/bb1ddba4-253d-478c-ac58-0abb23775000