Actually for a site-to-site openvpn just between two nodes, a shared key setup is much, much easier. No need to make or export certificates. Also that guide seems to have been written a long time ago against 2.0-RC1. The Guide for a multi-site PKI setup on our doc wiki may be more accurate: http://doc.pfsense.org/index.php/OpenVPN_Site-to-Site_PKI_%28SSL%29
Actually one thing that guide doesn't mention is if you do SSL/TLS and it's still just between two sites, if you just use a /30 for the tunnel network, it does not require that you add the client-specific overrides or anything like that. You can't push settings to the client, so you do need to fill in the tunnel network on both sides, and you need to fill in the 'remote network' fields on both sides.
It's much simpler to do shared key though, as described here: http://doc.pfsense.org/index.php/OpenVPN_Site-to-Site_%28Shared_Key,_2.0%29
Though even that is a lot of detail, it really boils down to:
On the server:
Add the server entry, set to Peer to Peer (Shared Key)
Set a tunnel network
In remote network put the client side LAN network
Add a wan rule to allow traffic to the wan address on the port (probably 1194)
Add openvpn firewall rules to pass traffic inside the tunnel
On the client:
Add a client entry, Peer to Peer (Shared Key)
Enter the server IP and port
Uncheck "automatically generate" and copy the shared key from the server screen to here
Set the same tunnel network as on the server
Set the remote network to be the server's LAN network
Add openvpn firewall rules to pass traffic inside the tunnel
The guide goes into much more detail than that, but I probably set up 6-10 of these things a week for people and it works every time…