Just opened my copy of The Witcher2 and was surprised by the Quest Handbook that was included. Is it necessary to reference the handbook in order to play the game?

no

I would suggest hiding it away and not falling for the temptation of ever using it.

Burn it for purity.

I haven't looked at it yet, but i have to say getting that and the soundtrack with the game is pretty fucking awesome.  Most guys would roll that into a collectors edition and make you pay an extra $10 for that.

Like other people in the thread I would actually suggest against using it at all.

It's way more fun finding things out by yourself, everything can be completed without it, and ingame quest descriptions give plenty of information, as well as you having to pay attention to dialogue anyway.
There may be 1 or 2 places where a couple of quest don't offer a straightforward solution, but again with just a bit of time they too can be solved by yourself with some thought.
 
The PC digital versions came with a pdf  of a similar handbook, I only used it on my second playthrough when I play like a completionist and comb through everything I might have missed on my first run.
But it's not necessary to reference it to play the game at all.

Not is not necessary but it is useful. I've been peeking in it when I get stumped on a side mission.

I didn't think I needed to use the guide, and will resist the temptation to use it. Unless of course I am stumped.

Still Tat's pretty cool they added that with the game, most publishers subscribe to the 'your on your own' mentality. Take for instance any EA games' joke of a manual.

Thanks for everyones feedback.