How much faster would optical computation be?
I studied optical computing in undergrad. From that, certain categories of problems would be solved MUCH faster. For instance, do some research on 4-f optical correlators. These kinds of operations can perform at the propagation velocity of light through the media (so essentially the speed of light). 

In terms of computing as we know it (logic gates, stateful gates which hold charge interpreted as '1' or '0'), I do not know if the advantages are there. 

That said, consider the economic momentum of "traditional" computer development with silicon chip fabrication. It's about 50+ years or so old. So (like other technologies), until any other technology is cheaper or in more demand, it will be a while until optical computing becomes a commodity. 

In any case, it's as cool as heck!