Today for short runs under 15 meters there are two common options: CX4 copper and SR (short range) fiber. The difference between them is essentially the cost of the fiber optic module. Today the most common module for 10GbE is the XFP, soon it will be SFP+. There are three sources for SR optics under $700 listed on our optics page. Optics are required on both ends so this makes fiber typically $1,400 more expensive than CX4 copper. Also copper adapters require less support logic and as such are often less expensive.
Single port copper NICs run in the $700-$1,000 range while similar fiber NICs are $800-$1,200. The expectation is that SFP+ fiber modules will be roughly 25% less expensive than XFPs so this will make fiber more affordable in the second half of 2008 as SFP+ gains traction. The real knee in the 10GbE adoption curve though will occur when the next generation of 10GBase-T products hit the market in early 2009. The current generation of 10GBase-T silicon requires far to much power to make it practical. This second generation of 10GBase-T will allow people to use cables and connectors they are familiar with, ex.Cat6E and RJ45, to attach servers and switches within 100M without the expensive CX4 cables or the optics required today for fiber.
Finally most of the 10GbE NIC vendors are on their second or third generation silicon. By early 2009 most will have trimmed and tuned things to the point that they will have, or soon support LAN on Motherboard solutions. When this happens we will see high end servers with 10Gbase-T support built in and 10G will then truly begin to replace GbE in the enterprise. We expect that this will likely begin to become common as we enter 2009.