Just read about Justniffer on UbuntuGeek and decided to give it a whirl. Downloaded deb installer from SourceForge and ran with:
justniffer -i eth0
I received the following output showing a few web connections and a telnet session to a mail server.
192.168.1.100 - - [27/Oct/2010:21:33:52 +0100] "GET /wikipedia/en/b/bc/Meta-logo-35px.png HTTP/1.1" 200 1611 "http://en.wikipedia.org/wiki/Main_Page" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.41 Safari/534.7"
192.168.1.100 - - [-] "" mailserver.domain.tld 0 "" ""
192.168.1.100 - - [27/Oct/2010:21:34:40 +0100] "ehlo jonny" Hello 0 "" ""
192.168.1.100 - - [27/Oct/2010:21:34:01 +0100] "GET /safebrowsing/rd/ChFnb29nLXBoaXNoLXNoYXZhchAAGM2gByDgoAcqB07QAQD__wcyBU3QAQAB HTTP/1.1" 200 173 "" "Mozilla/5.0 (X11; U; Linux x86_64; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.41 Safari/534.7"
192.168.1.100 - - [27/Oct/2010:21:34:55 +0100] "MAIL FROM: jonny@mydomain.tld" OK 0 "" ""
192.168.1.100 - - [27/Oct/2010:21:35:09 +0100] "RCPT TO: jonny@domain.tld" 111.222.111.222 0 "" ""
Possibly of use and for future reference when troubleshooting network issues.