I set up my nice Pi a few days ago. It seems to be going fine, despite me only measuring 4.6 volts between TP1 and TP2.
I bought a D-link DUB H4 which I am using to power the Pi via a 'Y' cable and for the keyboard and mouse (I should have got the 7 port version though).
The open circuit output voltage of the hub is 4.94 volts, whether it's measured at the psu, port or at the end of the 'Y' cable.
The keyboard and mouse are 100mA and 50mA so the hub supply is well over-specified.
Where could my voltage be going please?