USB 3.0 is also known as "Super Speed" for a reason. It's 10 times faster than USB 2.0. USB 3.0 transfers data at a nominal rate of 5.0 Gbit/s.
Almost all new USB 3.0 products are backwards compatible with USB 2.0 ports. So upgrading to new a USB 3.0 camera or capture device does not require a USB 3.0 enabled computer. That being said you won't be able to take advantage of the USB 3.0 speeds without a USB 2.0 port. "Type A plugs and receptacles from both USB 3.0 and USB 2.0 (or earlier) are designed to interoperate." - Wikipedia http://en.wikipedia.org/wiki/USB_3.0
3. Future Proofing
There is nothing worse than purchasing a new electronic device only to find out it's been replaced by a faster sexier model. USB 3.0 products are not likely to be replaced anytime soon.
4. Increase Functionality
USB 2.0 is only half-duplex that means it can only send communication one direction at a time. USB 3.0 is full duplex meaning it can send signals in both directions. Although real world product's are still being developed. Expect to see two way communication features using a single USB 3.0 connection.
5. Increased Bandwidth
As demand for bandwidth increases USB 3.0 is probobly over delivering for our current needs. Sure 1080p video at 30 frames per second requires bandwidth levels above what USB 2.0 can handle without compression but consider the bandwidth required for devices such as USB Hubs.