My experience with LG is that despite their specs being good, their build quality isn't really top notch. I've had numerous friends, and myself included, having their LG phones break on them in some form or another (usually screen cracking without external damage) without any dropping or impact of their phone. That, and the included hardware (like the camera) may sound nice, but it's actually of lower quality than those you would find on say a Sony Ericsson phone. Search up videos recorded from the LG Optimus 2X's camera and compare it to the Sony Ericsson Xperia Arc. Despite being of lower resolution, the Xperia Arc's camera quality is a lot better.
The 2nd core will eventually come into play, but not right now. Dual-core phones are just beginning to appear on the market, and it'll be probably another year before developers really start optimizing applications for that 2nd core.
I would actually hold off on getting the LG Optimus 2X if you can wait even another couple of months. Samsung is about to release their Galaxy S II phone(s), and they show some real promise with an amazing screen quality along with a dual-core processor. HTC will also be releasing their dual-core Sensation sometime soon as well. There will also be 3D-without-glasses dual-core phones coming out in forms of LG Optimus 3D and HTC Evo 3D sometime in the next few months if you're into that department. I'd wait a bit longer for a couple more options to arrive, as I honestly think that the Galaxy S II or HTC Sensation would be quite a bit better than the Optimus 2X.
