Are T-SQL SELECT statements outside of transaction grouping (BEGIN / COMMIT) affected in any way by the current value of SET TRANSACTION ISOLATION LEVEL?

There is some discussion (heated debate?) that all stored procedures used for reporting only should include the statement:

-- SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED

Some maintain that there is no effect at all unless the SET is followed by a BEGIN / COMMIT transaction pair.

Others feel that the effect of 'READ UNCOMMITTED' in a read-only transaction is the same as a naked 'SELECT' with no SET or BEGIN / COMMIT.

Finally, a few feel that including the SET...UNCOMMITTED statement for stored procedures used for reporting is the 'only way to go'