The advantage for gamers is that many titles still aren't properly written for dual-core operation; in this situation a single brute-force, high-frequency core gives better performance. So when the second core is idle, the dynamic acceleration feature can increase clock speed.
Higher frequencies mean higher power consumption - something that it's vital for a laptop to keep under control so that heat build-up doesn't become a problem. But since the second core is idle it can shut down, which keeps the total power consumption of the CPU within its specified power envelope.
The new chips are aimed at a niche market; Intel will not introduce any more Core 2 Extreme processors with two cores for desktops but will produce higher-speed quad-core chips for gamers and workstation users.