The latest episode, SKP14, of the SkypePodcast focuses on security, so may be of interest to folks here.  Sasha (the host) also gives a mention to our own Dan York and the Bluebox podcast.

Sasha quotes Skype CSO Kurt Sauer justifying why Skype jumps around different IP ports, making it hard to detect or block:  “One of the reasons Skype is difficult to find is that the people who provide the carrier services [ISPs, telcos] are in competition with Skype,”

You can find the full version of this quote in a Techworld article.