OUTPUT Clause

This one gives you access to the inserted and deleted tables in normal SQL so you can write statements like:

DECLARE @changes TABLE (
    ProjectId int,
    Name nvarchar(max),
    Description nvarchar(max)
);

update dbo.Projects
set Billable = 1
output
    inserted.ProjectId,
    inserted.Name,
    inserted.Description
into @changes
where Billable = 0

WRITE Clause

Allows more efficient updates of varchar(max), nvarchar(max) and varbinary(max) columns. For example:

declare @update_text nvarchar(max)
set @update_text = ' ... this is added to the end'

update dbo.Projects
set    Description.write(@update_text, null, len(@update_text))
where  Name = 'Timesheet'