Buying duo vs. quad core processor

Depends on what type of games you are trying to play and if you are looking more for batter life. I am a big believer in getting something in your budget and then putting in a SSD drive. You'll notice more of a difference in that than with a quad core mobile processor unless you are trying to do heavy gaming, video, photo, and other process intensive things.

What are you looking to do with your new laptop? I know gaming... but what type and what other things?
 
Notebooks are not for games, tough some very expensives ones run games fine. Hardwares trends for games are desktop quad core processors. If you need a notebook then get a quad one.
 
A quad core can come in handy for games that can actually use more than 2 cores. However, if you are choice on laptop based on price limits you to:

A. Dual core CPU (like the i5-2410m) and a fast video card (nVidia GT 560m), or
B. Quad core CPU (like the i7-2630QM) and a slower video card (nVidia GT 550m)

I would pick option A. More cores do not make up for a slower video card in most games.