I have a 13" MBP connected to an HP LP2475W, and the monitor has it's own powered USB bus which I use to connect a wireless keyboard and mouse (and a USB from MBP to HP to drive it). Sometimes - not always - I get a USB device low power warning when I wake up the MBP and the mouse doesn't work. I unplug the USB from the MBP, plug it back in, and it works fine. Occasionally it takes two or three tries before it works. Am I missing something here? Does it take a while before the MBP USB power comes to life?