I use Skype extensively, not used YM at all, but Skypes Video and Speech is far superior to MSN messenger and the speech also. Skype is improving its service on an almost weekly basis.
I can also highly recomend the SkypeIn service. I pay 30Euros for a UK number (I also have a HK and USA number but thats not the issue here). My family who are totally computer phobic can simply call the London number for free (BT together or something) and it calls my Skype PC.
Even if I am logged onto three PC's at once, they all 'ring' and the message "Parents Home" pops up on the screen. Even better is that I have Skype call forwarding. So if I am not on my PC, the number gets forwarded to my Hong Kong mobile. They don't get charged anything, I get charged about 3 Euro cents a minute. Of course if I am in China, I forward the number to my China SIM. No one needs to know where I am.
Now if I could just get them to pick up the damned phone and dial!
Oh yes, I use a Logitech messenger webcam, the reason is you can always download the driver. Get a dodgy Shenzhen cheapo and you might not be able to download a new driver. If you are like me I lose the disc 5 seconds after opening the Box.