Internet VPN is limited by the use of encrypted tunnels. This means that as the number of sites increases, the number of tunnels that require management and support increases. We would suggest that when in excess of 30 sites, internet VPN technology becomes unwieldy and a Managed IPVPN network might be preferred for simplicity and scalability.
However, this is not true of supporting ad-hoc remote workers. Large numbers of home workers can be supported using a simple IPSec or SSL VPN gateway system; these networks scale well to hundreds, if not thousands of users.
Encryption also makes it difficult to monitor the network and provide QoS technologies.