I don't work for Cisco, so I can't speak to how they will deal with OEM GBICs in the future, but here's how they handle it now:
http://www.cisco.com/en/US/products/prod_warranties_item09186a00800b5594.html
Basically, it's like how they've handled compatible memory and cables for years. If you choose to buy allegedly compatible GBICs, and they work for you, and you never have to call Cisco for support, and you save some money in the process, then great! Pat yourself on the back.
But if the third-party GBICs fail to perform as desired and you call Cisco for support, don't be suprised when they cut you off. Once Cisco learns that you're using third-party components, if they even THINK that that's what is causing your problem, then they are no longer under any obligation to help you solve your problem. You are on your own.
Yes, Cisco enjoys really high profit margins on memory, cables, and GBICs, to be sure. But buying from them accomplishes two things: it gets them to warranty the whole product, which cuts down on finger-pointing when things aren't working; and it it helps pay for the best tech support in the world, which gets you web sites like this where you can ask questions and get answers for free.
That being said, if you purchase third-party GBICs, I recommend that you test them thoroughly and trust them before you deploy them. Because YOU are ultimately the one responsible for guaranteeing that they work.
Hope this helps.
