Did it happen with an upgrade? or after installing something? Or just suddenly (out of curiosity)
Basically it's telling you that you have plugged a USB device into a port that is slower than the device. I.e. USB 2 device into a USB 1 or 1.1 hub.
So either you have USB 1.1 hubs on your MB OR possibly you do not have Windows 7 (or Vista) compatible motherboard drivers
installed and a generic USB 1.1 driver
is installed instead.
So either disable the warning as mentioned above or try to locate Vista usb or "motherboard" drivers for your machine and see if those install better USB drivers so you can get 2.0 functionality from your devices.
Also, in addition to what DJG said, DO go to your "USB Root Hub" entries in device manager, right click, Properties, Advanced and see what it says under hub information. It should say "High Speed" for USB 2.0 operation. If it says "Full Speed" then it is either a USB 1.1 hub or is acting like one.