I have two in constant cycle. Not really used as a PT anymore, but still offers a handy way to charge. A friend of mine dropped my eGo-pt and dented the end cap up, still charges and lights up fine however.
If it ever stopped charging through the USB, you could always purchase the 510 extender for a few bucks and charge it off of a 510 charger. The output is 4.2volts but the amperage is a bit lower at 150mA, might take a bit longer to charge as I believe a USB port puts out approx 500mA (unverified).