A Billion Bits Per Second → Could network cards keep up?

Ok, perhaps I haven't been keeping up with the latest in PC hardware, but doesn't the average network card run at 100Mbps? So even if the cable companies gave you 1,000Mbps, your PC would only be capable of sending and recieving data at 100Mbps. If so, what's the point of any bandwidth increases beyond 100Mbps?

EDIT: A quick check of NewEgg shows 10/100/1000Mbps network cards for under $15. I'm betting that the average computer in use today sports a 10/100Mbps card. By the time they roll this out, however, the 1000Mbps cards should be predominant. (Or, at the very least, you'll be able to easily upgrade your PC to support those speeds.)

My motherboard has a built in gigabit port. I all ready for it;).

Also, consider the fact that most on board Nic's are part of the PCI bus, and it could become overloaded very quickly. If someone has a sound card, NIC, and nothing else they could still in theory use up all the bandwidth on the 133Mhz bus and start to have problems. You are correct that most computers now ship with a 10/100 NIC and some of the newer models have built in 10/100/1000 ports.

But even if the user was to get the full speed from the company they would have a hard time reaching the full speed on a consistent basis. Until storage tech reaches higher speeds anything past 100MB/s really won't do much good since the drive controllers usually cannot send or receive data much faster.

The PCI bus on most computers runs at 33mhz and is 32 bits wide. This means the PCI bus runs at about 133MByte/second. Most onboard peripherals don't use the PCI bus. They are directly connected to the southbridge. The PCI bus is connected to the southbridge as well, but PCI bandwidth is not used when the PCI bus is not used. The northbridge takes care of the AGP bus and system memory if the CPU doesn't have an onboard memory controller. The southbridge is connected to stuff like firewire, USB, hard drive controllers, parallel ports, PS/2 ports, RS-232 serial ports, sound cards, network cards and other stuff. The link between the northbridge and southbridge depends on what chipset is being used. Most of the newer VIA chipsets use 1066MBytes/second.
Not everything needs to be written to the hard disk. Streaming video and audio are examples.

And interestingly the speed of my broadband connection is the reason that I haven't switched to 1000Mbps networking equipment.

Also, harddrives can't write data that fast either. That would also slow you down on a 1Gb connection.

Say you only have a 100mbit network card, but you have 5 computers each with their own NIC. So you get a gigabit switch, or one of those 10/100 switches that has a gigabit uplink (haven't seen one of those in awhile though) and use that to share the connection to your broadband. I'll grant you that that kind of bandwidth would be insane by todays standards but I'm merely pointing out that it would be possible to go beyond 100 mbit/sec.