i had problems at first but it was due to a driver problem. i use windows XP. i can use it both via usb and bluetooth, though much slower with BT but with USB the phone gets very hot as it's charging with too little power.
it's an awesome feature, like if your texting with someone you can write way faster, perfect when you're at work.
i've read about that some people had to use usb debug to make it work but i don't. make sure there's no yellow exlamation marks in the device manager, cause then some drivers aren't properly installed.