This tool (Ethereal at the time) was absolutely invaluable to my job as Senior Tech Support of Weblogic family of products. I even got clients to run it and was able to provide solutions like "your large JDBC connection pool had all its connection silently dropped by a network firewall (that client was not aware of) and that's why you having 1 hour transaction delay on first one in a morning. Every pooled connection had to timeout and reset". And "Internet Explorer would abort a TCP connection for already-cached resource and that generates non-standard network level errors on your IBM server' Weblogic installation"

I lost half of my hair on that job. Without Ethereal, I am sure I would have lost all of it and a lot more of my sanity too.