Did you search the WiKi? Or the forum? The answer is Yes and No.
You can have up to 5 WAN ports, no problem. Making them work the way you want - well, that would be nice, but so far no one has managed to be happy with it.
Yes, it is possible. I have set up my GL as a dual-WAN router, although it was a bit problematic because different routers have different port numbers, and simply applying the solution from the Wiki didn't work. There's another one for manual switching between to WANs. I found my router's port mapping on [url=wiki.openwrt.org]OpenWRT Wiki[/url] .
I don't need load balancing, so I didn't use the firewall scripts from the Wiki. Neither do I need manual switching. What I needed was just static routing and automatic failover. I achieved both by simply making a startup script with static routes and an additional default gateway with a higher metric.
One of my connections is a PPPoE, another (the additional WAN) is a static IP. So far it works as intended.
The problem is firewalling the second WAN though. My knowledge of Linux and IPTABLES is next to non-existent, so I spent quite a few weekends on this, and can't even tell if it works or not.