Is it OK? Or does it hurt anything?
I do it all the time and hasn't hurt my phone at all. Don't try this hooked up to a usb though, as I don't think there is enough juice through the computer to charge it while you use it.
i didnt think so either but when i connect it to my usb port it shows charging :s but i only did that once ill have to try again and see if its just maintaining battery level or actually charging
It's best to use a powered USB hub, then to plug directly into the USB on your computer, if possible. I find that my HP laptop will sometimes have difficulty keeping up with the Droid power requirements when using and charging a dead battery.
On my powered USB hub, however, it doesn't skip a beat.