logNameFormat is used when windows security is active to help name the session log file. A String.Format is used with this setting's value as the template. The userid is parameter {0}, a DateTime.ShortDate string is {1} and a full DateTime.Now object is parameter {2}. Note that if the format is simply "{0}" then a log file will have ALL logging for ALL TIME for the given userid. A nightly sweep and archive of logs can avoid the log file from becoming too massive...
Examples:
<add key="logNameFormat" value="{0}_{1}_{2,-14:HH:mm:ss}"/>
Will create a log file name like: DOMAIN_USER_3_1_2013_15_04_40.log on March 1, 2013 at 3:04:40pm: will log all entries for this session.
<add key="logNameFormat" value="{0}_{1}"/>
Will create a log file name like: DOMAIN_USER_3_1_2013.log on March 1, 2013: will log all entries for a given day.
<add key="logNameFormat" value="{0}"/>
Will create a log file name like: DOMAIN_USER on any day--will log all entries for this user until deleted or moved!