When you use a gigabit switch, it is a point-to-point link between the switch and the device. Your switch doesn't have a maximum bandwidth of 1Gb/s spread out or shared to all the ports... it's a point-to-point connection at the advertised speed. Each port on the switch has a maximum speed of 1Gb/s... so if you have 8 ports, then the aggregate speed of the switch would be 8Gb/s. The only way bandwidth is ever shared across all the ports is if you have an ethernet "hub" and not a switch. I don't think they even make hubs anymore.
If your PC has a 1Gb/s NIC, then again... it's a point-to-point link with the switch, and the maximum bandwidth is available to it, even if you have massive amounts of traffic going over the other switch ports. Now, if you have a really cheap switch then you may not enjoy the full aggregate speed over all the switch ports, but even cheapo $25 gigabit switches can easily provide the aggregate speed. I've had data transferred from one PC to a server at gigabit speeds, iSCSI transfers at gigabit speeds, recording 6! cablecard streams, and watching netflix and torrenting all at the same time, without any loss of speed... all on a cheapo $25 gigabit switch.