Typically, you are only logged in to one machine. If you had been offline when you log back in new voice mails are delivered. If three VM's were delivered and you listen to two and then go and log on to another PC with the same identity, you will receive a copy of the third voicemail you hadn't listened to. This means that listening to a voice mail clears the Skype server and confirms delivery of the message. Until you listen it will send you that VM every time you log in no matter where you log in. Once you listen it stops trying to follow you.

How do you use this knowledge?
If you want a central repository for all your VM then either just use one PC or leave that PC on at all times. Thus, if you are out of the office on a laptop, and normally use a desktop then leave your desktop on if you want to capture all the VM there. Listening on one won't delete the message from another.

What are the implications?
You could share VM on a partyline. It would be just like it happens now on the home answer machine. However, you would have to be always on... to share in all the messages.

This creates a very efficient messaging server for Skype, purging messages in many cases as soon as they arrive. Unlike cellphone systems that request you to press 7 to delete or only save for 30 days. Skype simplifies this behavior. I'm sure all voice mail also remains encrypted. Thus the Skype is merely a delivery agent.

It's useful to remember that Skype is unique as a IM system in that it doesn't log you out of one client when you log into another (like AIM, Yahoo, MSN). Also remember that your contact list now follows you. So no matter where or on which machine you log on... you will always have your buddy list.