Quarantine is the most interesting technology to protect your company against attacks coming from the VPN users. There are a lot of good technical reasons to implement it.

Another good way to be convinced by this threat is to check the articles and surveys done by well known companies.

Here is a list of surveys and articles you may check to make your final desision.

  Industry Partners Demonstrate Broad Support For Network Access Protection Technology From Microsoft

"Microsoft anticipates that the initial release of Network Access Protection will be delivered with Windows Server "Longhorn," the next version of the Windows Server operating system, due to release in 2007."

The Gartner made a lot of surveys about remote users threat, quarantine, ...

  Strategies to Combat Rapidly Spread Cyberattacks

  Don't Wait for Cisco and Microsoft to Scan and Block Attacks  

  Protect Your Resources With a Network Access Control Process

  Market Statistics: Enterprise Routers, Firewalls and VPN Equipment, Worldwide, 2004 (Preliminary)

  Network Access Control Market Overview

  Security Software Market Forecast, 2003-2007 (Executive Summary)

  Making Sense Of Network Quarantine

  Choosing The Right Network Quarantine Solution

  Relax: Cisco And Microsoft Won't Clash On Network Quarantine

  Cisco's Self-Defending Network: Not Yet

  VPN Sales Are Strong, With AT&T In The Leat

  Mobile VPNs: Securing Mobile Remote Access

  Endpoint Security: Network Quarantine's Dark Horse