The first thing to realize about dual-core processors, is that few people actually need them. Two processors won't increase the performance of games, but it is very helpful if you like to multitask. Dual-cores are perfect for someone who likes to run several high-end processes at once, but if you're a single-minded person, they won't benefit you.
That being said, the new Intel Core 2 Duo is an amazing processor. While they're a bit expensive right now (not to mention supply and demand tells us they'll be out of stock for awhile, now), they're incredibly energy-efficient, as a 2.4ghz Core 2 could rival most AMD processors on the market. While the higher-level models of the Core 2 (I'm looking at you, Intel Extreme), are too expensive for any but the most die-hard gamer, the 2.3, 2.4, and 2.6 are all well-priced for the performance they put out.
One problem with the Core 2s, like all new technology, is that compatible hardware is, while not difficult to find, certainly takes a bit of searching. Specifically, motherboards that are compatible are a minority right now, and there are even fewer that support Crossfire. You won't find a non gaming-grade mobo that supports Core 2, and the number of mobos that support Crossfire AND Core 2 are very limited (ASUS makes a great gaming-grade mobo as seen
here that supports both).
Anything else you need to know, Zaak?