HTC EVO owner here:
Bought a cheap Ebay combo battery charger/USB port phone charger device.
As others indicate, the phone interface locks up when the USB port of the charger is being used. My pet theory is that the power input is too low. Not much basis for it, other than the little battery animation graphic at the top appears to have a slower speed of battery filling than on my other chargers. Also, the charger doesn't get very warm - implying there's not much power flowing.
No damage to the phone, I've let it completely recharge my phone in fact. It will continue to recieve and display text's/calls/etc. It's just that the interface stops responding. Annoying, but not a big deal. I suppose I could demand another one from the supplier, though I figure it'll just be the same.