Some of our Field Engineers, Kal Yella and Denzil Ribeiro (@DenzilRibeiro) have posted a blog that discusses how to optimize adding a partition when either the right most, or left most partition is not empty..  It is well worth the read, so we are posting it on PSSSQL to help get it out there.

Oops… I forgot to leave an empty SQL table partition, how can I split it with minimal IO impact?
http://blogs.msdn.com/b/sql_pfe_blog/archive/2013/08/13/oops-i-forgot-to-leave-an-empty-sql-table-partition-how-can-i-split-it-with-minimal-io-impact.aspx

Venu Cherukupalli - SQL Support Escalation Services
https://twitter.com/cherku