i think another factor that distinguishes skype (and joost, and xobni, etc.) as not inherently "web 2.0" is serious secret sauce/engineering under the hood (protocols, algorithms, search, scalability, etc.) see http://www.blackhat.com/presentations/bh-europe-06/bh-eu-06-biondi/bh-eu-06-biondi-up.pdf -- very cool stuff (anti-reversing protection, crypto, clever protocols, etc.)

one of the biggest drawbacks in the web 2.0 world from a business perspective is that often the technology provides little barrier to entry. with the typical web 2.0 idea you're not competing on technology but rather on distribution/PR/marketing/engineering user adoption -- things most hackers aren't inherently good at.

one critical point of leverage that good hackers have is the ability to provide solutions to hard engineering problems that are usable and valued by normal people (google, skype, kazaa, bittorrent, etc.) conversely, if you're not solving hard problems, or are solving hard problems that normal people don't care about, your advantage as a good hacker is diminished.