The following picture shows an OmniGraffle palette I put together for doing network diagrams. It may be useful for others.
You can download a Zipped archive containing the palette by clicking on the picture. The download is 192Kb in size.
Send comments to me using the link below. Just realised that the email address that has been on this page for a while isn't used anymore. Sorry if you emailed me and didn't get a reply.