My only experience is with a GB Pro that had failed communications with the other node boards, effectively keeping the game from booting. This is a route game; so no revenue for about 3 weeks. The node board failed under ownership of the second operator at about 11 months after it was initially put on route by the first operator. Luckily, in both cases, I knew both operators and the distributor. When I initially called Stern I was told they only replace the boards for about 6 months, so basically SOL. I then contacted the distributor and had a replacement in the mail. But if this board fails again, I'm not sure, but I think it'll be time to pony up.
Seems like Stern is stepping up and replacing the node boards when they fail, which is a good thing. I doubt this will continue to happen indefinitely, which makes me wonder, how many people have had a replacement node board fail? Was it still replaced under warranty the second time around?