A recent OpenSSH version added support for TUN devices under Linux, Windows and I believe a few other operating systems. With VTLs, you lose a few of the features of the 'local' network like button status and other goodies. Since you can setup SSH to do layer-2 now, you could in theory have decent multi-site support that is encrypted across the internet through one port. It would bump up traffic going back and forth quite a bit between sites, but it just might work.
You could also do the same type of thing with OpenVPN, but I'm more comfy with SSH so far.