Funny enough, the thing that had me thinking the most was the double ethernet ports. What would that be for? Two different networks? When one cuts out you just switch to the other one?
Number one would obviously be to connect to two different networks. It could also be useful in a scenario where the machine is used as a server and you want a semi-redundant backup network line. It could also be used to directly connect to a NAS box via Ethernet.
[0] by real world I mean on a properly configured network. Many companies don't have that though so you often see "gigabit" speeds in the 30-50MB/s range.
10gbps is expensive, uses a lot of power, requires cat6, and rare outside of servers and SANs currently. Interestingly enough, there's a recent 5gbps spec that works with Cat5e that might be picked up by OEMs to replace 1gbps. Still no chips or cards out yet, so it will probably be a while. In the meantime, bonding two 1gbps interfaces gives you about a 200 megabyte/sec write & read speed off a SSD based server/NAS.
40GbE is probably overkill, right?
Not at all. :)
If you're working on video over the network you can use two ethernet cables for faster network access