I have run across issues running PPTP as a VPN server. Easy to setup, yes, but so far I have had errors using the built-in PPTP server @ windows 2008 r2, namely, connections are dropped and the client does not show it has been dropped. I am trying now draytek's VPN solution but I'd rather use something that integrates with AD, and is robust.
I came across SoftEther VPN, looks promising, but would you use it instead of openvpn ?