I need to make an array of eight 720p webcams that take pictures at the same time (much like the Google streetcam). It seems to me that the best way to do this is by using two of these with my eight usb cameras.
That should work out okay.
As far as taking pics at the same time goes, that would depend on your camera's software. Some have better software than others.
There are some free ones or shareware ones on the web also.