As I was implementing the XMLRPC Services for the Wordpress API I was struggling with figuring out how to debug it. At first I was using wireshark (a packet capture tool), but that was capturing a bunch of packets I didn't need to see as well as not pairing request with responses. Then I found the answer, a Firefox plugin called Tamper Data, very easy to use and very powerful. Anyway if your developing any sort of web service or perhaps doing ajax development I recommend it.