Just take a look at the following screenshot I just took, showing two Skype 5.3.0.116 instances running on a current Windows 7 box with 4 GB of RAM:
That’s 330 MB of private memory for each instance at this very moment! Note that these numbers are steadily growing (at about 2 KB/s) for both processes – for no apparent reason. A hint, that there’s likely a memory leak somewhere in Skype.
Let’s hope Microsoft will rewrite Skype from scratch (The current code-base probably isn’t worth refactoring). I’m confident they don’t lack the human and financial resources to do it. It can only get better.