First benchmarks show that the new Atom N450 doesn't really bring more performance to the netbook world: processor core, caches 512KB) and clock (1.66GHz) don't differ very much from Atom N280. The only architectural change with impact on performance is the integrated memory controller: this allows memory access with a significant lower latency. On the other hand hyperthreading works less efficiently with lower memory latency, in fact hyperthreading uses the CPU memory access stalls to alternate execution between the two threads.
Intel Atom N470 is clocked at 1.86GHz and got the same N450 technical spec, actually they share exactly the same design/gates.
What is the performance improvement that we will get in the Atom N470? The 12% higher clock will be visible in benchmarks, improving performance linearly up to 12%. Nothing revolutionary, Intel Atoms are CPUs designed for low power and low cost. It's in Intel interest to maintain a certain performance gap between the cheap Atom and the CULV processors. In any case Atom N450 and N470 are not able to decode HD video without some external accelerators (such as BCM70015).
Intel won't significantly improve Atom performance as long as some serious competitors appears in the netbook market: this year something can move with the upcoming netbooks (smartbooks) ARM Cortex A9.