Just a quick note that we again can modify whether system messages are to go to eventlog/errorlog again. I.e., we can change the is_event_logged column in sys.messages. This is very valuable in general and specifically is you want to define Agent alerts (for which Agent polls the Eventlog). For instance:
SELECT * FROM sys.messages
WHERE message_id = 1205
AND language_id = 1033
Notice the value for the is_event_logged column. Now, run below:
@message_id = 1205
,@parameter = 'WITH_LOG'
,@parameter_value = 'true'
Now, re-run the select statement and see that you modified the behavior for the system message. Now, re-run the sp_altermessage with 'false' to reset to default.
The ability to modify this behavior for system messages was available prior to SQL Server 2005, but some re-architecturing in 2005 removed the functionality. kozloski informed me in this blog post that 2005 sp3 re-introduced the functionality and obviously as of sp1 the functionlity is back in 2008 as well.