Maximum Number of USB Web Cameras?

My computer setup:
17" Macbook Pro
3 USB Ports
2 Firewire Ports
2.2 GHz i7

So I’ve read that trying to use more than 2 usb web cameras on the same hubs will cause issues. I currently use a Logitech Quickcam 9000 and Logitech HD Pro C910 in our setup and am able to switch between these beautifully, but trying to add a third camera source, say the built-in display camera, will result in just a black screen when trying to bring that source live.

Can anyone recommend a proven way to get a third and possibly fourth camera working in a setup such as this? Will a Express card USB hub enable the use of extra cams? Just trying to get a proven method without having to buy and test multiple products. We would like to stay with USB based cameras, but if firewire is proven to work in addition to 2 existing cameras, I’m willing to try that as well.

If you use USB webcams, BoinxTV will take the document resolution you specified and request this resolution from the camera to get the best image quality. If the camera can’t deliver the exact resolution, it will use the next higher resolution available. This might result in a high resolution and a higher data rate. Like this two cameras on the same USB Bus might be too much data for the USB bus at it is limited to 480 Mbps.
The solution is in most cases trying to get the two cameras spread on two busses (most Macs do have two busses).
Finding out which USB port belongs to which bus is a bit tricky. Connect one camera and open “System Profiler”, that you can find in /Applications/Utilities.
Select “USB” in the left hand column. Now you can see under which USB Bus you camera appears.
Now connect the second camera and go to Window > Refresh (or press Command+R)
The second camera will also appear in the list.
If it appears under the same bus as the first camera, plug it into another USB port until they are both on different busses. If they keep showing up under the same bus, not matter where you connect them, all your USB ports are on the same bus.