I've been using a MacMini running OSX Server to do VPN at my house for about a year now. It worked very well until I got my new MacBook Pro. Unfortunately, there have been problems since then. I now have a call into Apple and a nice work-around.
I'm not the only one with this problem, by the way, it seems to be a problem with the PPTP negotiations and I believe it's an endianness issue. The crux of the issue is that I can connect, but exactly a minute later the connection drops (everything works fine in the interim).
Digitunnel installs as a System Preferences Panel and functions to start and maintain the VPN, including some more accessible options than those available from Apple. On the OS X server and client solution, the client cannot determine the routes that are used for the tunnel. With Digitunnel, the client can add a list of arbitrary routes (or send all data through the tunnel).
At $58, it's a bit steep for a simple work-around to a bug from Apple, but quite a bit less expensive than the more powerful VPN Tracker (which specializes in certificate-based security) at $89.