David,
You need to consider which Cox internet speed are you subscribing to. They are currently offering 1mb/s, 3mb/s, 18mb/s, 35mb/s, and 55mb/s packages but you could be grandfathered into an old package with a different speed (ie: 8mb/s, 12mb/s, etc). If you don't know what speed you have, go to a website like Speed Test (
http://www.speedtest.net/) and find out. Assuming you're not using your Internet connection to watch movies or download large files during the speed test, the results are usually fairly accurate.
You also need to consider the model of cable modem you were using before the upgrade. There's a chance that your previous cable modem was old enough that it still had a 10BASE-T Ethernet connection (approx 8mb/s throughput). Simply replacing the modem may have eliminated a bottleneck if your Cox subscription includes more than 10mb/s of throughput. In most cases, this would be a noticeable improvement.
We subscribe to 18mb/s service. I upgraded from an older cable modem with 10/100mb/s Ethernet to a Motorola DOCSIS 3.0 cable modem with 10/100/1000mb/s Ethernet earlier this year and also felt an improvement in speed even though the old cable modem shouldn't have been a bottleneck in my case. It could also be that these newer modems just perform better overall?
Until you are able to subscribe to 100mb/s or faster service from Cox, I doubt you would notice an improvement in Internet speeds by upgrading your home switches/hubs from 100mb/s to 1000mb/s (gigabit). However, if you copy a lot of media (videos, cd images, dvd images, etc) between computers in your home, you could notice an improvement in local transfer speeds between those computers by upgrading from 100mb/s to 1000mb/s. Most computers are able to transfer data across the local network at speeds greater than 100mb/s, but few computers can take advantage of the full 1000mb/s (gigabit) speed because their hard drives become the bottleneck. Most hard disks are only rated for 30-40M/s (or 240-320mb/s) of throughput.
In short, the gigabit devices are becoming reasonable enough that it's probably worth upgrading, but you probably won't notice a performance difference unless you're moving a lot of data between your local computers.
Jason