With open source, the chances that somebody will catch a security flaw are generally much higher. It's not necessary for each individual user to understand the code as long as some people do.

I am not the only human being on this planet, you know (And if I were I would not need skype anyway).

Even if you can not read and understand the code you are still better off with the open source. Due to the fact that independent researchers or programmers unaffiliated with developers will be able to audit the code. While with the closed source software, the only information you have about the inner workings of the software is provided by the developing company.

I wouldn't be so extreme. It's reasonable to assume that a properly encrypted connection is secure form entry to exit. You would have to use proprietary tools only at the extremities then, which is actually quite feasible nowadays.

anyway: after learning that not even Osama wasn't even encrypting his shit my view on security is slightly different.