I was trying network-manager-openvpn plugin today on Lucid, I could import my configuration, DNS was set up correctly upon connection/disconnection, route imported correctly (almost :)).
One issue though is that it was also changing the default route to the VPN tunnel while this should not happen.
Well, the solution was simple enough after some googling (or yahooing should I say).
It appears that there is an option to set. And was as easy as editing your connection and going through:
IPv4 Settings->Routes and checking “Use this connection only for resources on its network”.