This effectively ties the client to a specific vendor's server at the moment, locking out a long list of interoperable PPTP vendors. Some of our users have opted out of IPSec simply because the certificate management required too much expense and administration effort. Like other vendors, Efficient Network is actively working the IPSec standard into both our client and server products for release in the near future. Most network administrators do their best to steer clear of proprietary solutions these days. Generally you should avoid any encryption protocol that requires you to buy both the client and server components from the same vendor.
Some vendors use proxy-based solutions which offer only a limited number of services for encryption.
Nor does it provide for tunneling of Appletalk or Netware file sharing traffic. Secure access that doesn't provide for file and printer sharing is extremely limiting in most enterprise settings. In a market study by Infonetics Research, PPTP was found to be the most popular VPN protocol currently in use. PPTP and L2TP will not go away. IPSec is clearly not ready for primetime.