That scheduler item is supposed to clear out the log.  However, I have enabled it on DNN v4.05.03, and it didn't clear out any records.  I ended up writing an archiving system of my own to maintain access to the site log items should an inquiry arise later.  However, I would suggest that you clear out your event log and begin going through the exceptions and fix the errors.  There is no reason that an event log should get so big.

Here is an SQL statement that can clear out your event log.  This will delete any records appended more than 10 days ago.

DELETE FROM [dbo].[EventLog] WHERE [LogCreateDate] > GETDATE() - 10

Please note that you should backup your database before running the above statement.  Also, I just wrote it freehand, so I might have the table or column names misspelled.

Yeah, you're right of course.  I had gotten jaded by the process about a year ago.  :(  At the time I had a handful of bugs that were apparently not reproduceable.

Here is my most current one:

http://support.dotnetnuke.com/issue/ViewIssue.aspx?id=6812&PROJID=23