Currently it's required at the end of a merge and the end of the statement prior to a CTE. REquirements may well increase in future as the T-SQL language gets more and more complex.
p.s. http://blogs.msdn.com/b/davidlean/archive/2009/04/06/sql-server-nolock-hint-other-poor-ideas.aspx
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability