I have Skype and have it on almost all the time that I am on the computer...which is a long time.
Having said that, though, I also don't have the sound on until I put my earphones on so if someone calls me I don't hear the ring. I do, however, see the Skype flashing thing so that I know I have a call coming in.
I don't use the video part of Skype where you see who you are talking to.
If I can't take the call or don't want to for whatever reason, the person leaves me a typed message and I get back to them when I'm able to. Which is usually soon after the original call comes - unless I'm not home.
I also like Skype for transferring documents.
I'm like Dom, though, I don't have just anyone in my Skype contact list.
And occasionally I will get an errant message from someone that I've never heard of. If that happens and you don't want to be in contact with them, you just put that person on block.
Also, a couple of years ago I was in a meeting on Skype and we heard someone talking that none of us knew...somehow that person was able to get in on our conversation. But that just happened once to me. I suppose it could happen to others a lot.
All in all, I like Skype because you really are the one in control with it.
Karen