I've set up openvpn server on my old N800 which I leave at home. I can then connect to it using my N900 on insecure networks and all the traffic goes through the secure tunnel to my home connection and then out onto the internet. It also means I can access devices that are sitting behind my home router and not made public.

Generic (not maemo-specific) setup guide:
http://openvpn.net/index.php/open-so...ion/howto.html
I used routing rather than bridging mode.

On my N800 (the server) I had to install iptables-ext and iptables-nat packages and install their kernel modules:
http://talk.maemo.org/showpost.php?p=89044&postcount=25

On my N900 I had to do this to make all traffic go through the tunnel:
http://talk.maemo.org/showpost.php?p=519753&postcount=5

It is quite a bit of work to set up, but now it's working, it's very easy to use and gives me piece of mind.