Sorry, but I consider PPTP to be a VN, not a VPN.

It might very well be so, but I bet that 19 out of 20 of those guests want to connect to their corporate networks using whatever 'Connection Wizard' on their Windows offers them, whether we call it private or not.

(BTW, your comment prompted me to look a bit around. According to this paper by Bruce Schneier of Counterpane, the one vulnerability left in the second iteration of MS PPTP is the fact that all keys are still derived from potentially weak password, making the whole affair vulnerable to brute-force offline password-guessing attack. Sigh, I remember when crypt() hash was considered adequate protection of passwords on Unix.... )