you can use fiber optics for gigabit ethernet.
However, the thing to remember is that GigE (1000baseT) works over Cat-5 just fine...
yeah, but the range is much more limited.
as for the bus being saturated, yeah again..
pretty much a few things have to be in place when gigabit ethernet is to reach the desktop (not just the backbone of a network). faster bus, and more selection of fiber gigabit NICs. 10 gigabit would probably be the killer app for fiber, though again, it depends on where you want to use it.
if you want fiber to the desktop you can get it, but it's only useful for long distances, making sure you dont' have to re-route new cable for a long time, and for extremely fast speeds that would saturate a normal 32/33 PCI bus..