Multiprotocol Label Switching Virtual Private Networks and the enterprise - Do they fit in the security model?

Multiprotocol label switching virtual private networks have gained press as a new service provider method to provide a secure path in the public Internet space. The question arises if this technology is the latest marketing ploy of the service providers or if this is a valid option for the enterprise within the security framework? If this is a valid option for the enterprise security framework is it a WAN technology only or does it have a place within the MAN or LAN environments? The first part in looking at the issue it to first understand if multiprotocol label switching virtual private network technology is a virtual private network and to determine how it works. A determination of what security is provided or not provided; also looking at what flaws it may have as a virtual private network. If the technology is found to be acceptable as a virtual private network, a look at how different enterprise customers can take advantage of this technology.