Just curious. I've never had anything against ads personally unless they're intrusive -- or that my data is being bought & sold to show them. Not that I trust $vendor to keep that data private, but showing me the latest advertisement for some movie coming out next week isn't going to ruin my experience. Youtube's advertisement implementation for example, I find intrusive & frustrating as it literally displays over top of the content and returns on every video you watch.
Until skype starts strapping a pepsi logo to my partner-in-chat's face, I'm content.
If it helps keep skype around longer, kudos. I enjoy using the app.
I agree that ads have their place, particularly in a free product or service. But since you brought up Google, I'm not sure we should be holding them up as an example of how to do un-intrusive advertising:
When you search Google, it uses Google's servers and web index.
Skype uses other user's bandwidth to route calls.
Leeching other people's bandwidth and also advertising to you while doing so, stings.
(Yes they have directory services and development to pay for, and yes they have infrastructure, for POTS-integration, but on the other hand, POTS-integration isn't free, it's already charged for separately on a service-use basis).