Quad-Cores are awesome (as long as its a fast one)
If you do a lot of Multi-tasking and video encoding/photoshop, you should take a Quad-Core, faster clocked dual-cores do better than a slower clocked more core Quad-Core but thats because the games are immature and they aren't developed enough for Quads... but within a couple of years they will get to utilize all 4 of the Cores of a Quad