Choose a VPN client that comes as close as possible to requiring zero end-user expertise. Seek out features like canned policies and automated push updates to remove the end-user from the equation. Doing so will reduce support calls and increase subscriber satisfaction. Test your VPN client in every desktop environment you plan to support. Document environmental requirements, supported adapters, and compatibility issues.
Nobody likes to waste time debugging a combo already known to be problematic.
Invest your time in software administration and policy management tools from the start. With the right infrastructure in place, you'll be able to scale with your customer base. Develop formal policies and procedures for VPN client administration. Applying them wisely and consistently is up to you. As embedded VPN clients become more widely deployed, leverage them.