I measured on the 5V pin to the ground and got stunned over the variance that I saw. First I had a Powered USB hub where my devices where attach and so the Raspberry. I just decided to remove my main power supply (mini usb), and noticed that the Pi where still running of the power from the USB hub (main USB). Here I noticed a voltage drop from 4.9 to 4.3 voltage.
Are there no compensating circuit on the bord that can maintain a "good" 5V?
Why I'm asking: Won't this be a problem if external circuits as ADCs and such are connected to the GPIOS?