Hi Roger,
By default, LTM doesn't log details for every connection to a VIP. You could do this using an iRule, but it will have a performance cost. Here is an older logging iRule example:
http://devcentral.f5.com/wiki/default.aspx/iRules/LogHttpTcpUdpToSyslogng
For 9.4.0+ you can use log -remote to send UDP syslog messages to a remote server. This should be more efficient than logging through syslog-ng. See the log wiki page and an article from Deb for details:
http://devcentral.f5.com/wiki/default.aspx/iRules/log
http://devcentral.f5.com/Default.aspx?tabid=63&articleType=ArticleView&articleId=190
If you can upgrade to v10.1.x, you could use the high speed logging (HSL) options for an even more efficient option:
http://devcentral.f5.com/wiki/default.aspx/iRules/HSL
Aaron