Ashamed to say that I've only clocked in a measly 5-6 hours by now. I don't think it's really necessary to have played the first game. You get a sort of brief summary of events that occurred before and they play somewhat into what you experience in the prologue. After that though, it's essentially a standalone game. Whilst you do meet characters that you saw in the first game, it doesn't really matter whether you saw them before or not.
Anyway, I've played long enough now to realise that my pc is definitely at the very bottom end of the minimum requirements spectrum. Rather than continue having a stilted, ugly experience I'm thinking of abandoning Witcher 2 until I've worked up the courage to shell out on that pc upgrade. Or in other words, bringing the Skyrim upgrade forward >.<