Paul White NZ (3/31/2010)
CirquedeSQLeil (3/31/2010)
Adam Machanic summarizes his testing here.In the comments, Adam notes that there seems to be no difference in SQL Server 2008...
I think that's him expressing himself badly - the figues he gives for SQLS 2008 indicate that coalesce is now measurably faster than isnull.
Tom