Just because something is popular (e.g. MySpace) doesn't mean something else can't come along and replace it (e.g. Facebook)

Everyone I know who uses Skype complains (eventually) about the quality.

Additionally, Skype is effectively a closed (in the sense of opaque) system controlled by corporate interests. Now, I'm not against someone making a fair return on a fair service, but I do worry about who has control over my information. Who is Skype accountable to?