Umm. No. It's not placebo as you make it out to be. Have you actually tried overclocking it to 1GHz or higher on your N900? You do know what the difference between 600MHz and 1GHz is right? If so, why lie to people with the above statement? (about it not making it more smooth/snappy/fluid etc)

I can easily show you the difference between 600MHz stock and 1Ghz on my N900. It is faster and more responsive. Totally noticeable in many everyday tasks. Even during sliding through the desktops. (Yes, it is supposed to be GPU accelerated. But CPU is providing the "data" to the GPU and the improvement definitely can be seen by eye.)

btw, seems these CPUs in the N900 have been made with quite a good yield and specification as many can run at ~1GHz without any issues. Yes, some people go on about it reducing its lifetime etc. (which is all theory btw. If the CPU isn't stressed enough, the lifetime of the CPU is near identical.)

If we had everything identical except upgrade the CPU to some dual-core 1GHz CPU, I'll bet that N900 will suddenly feel like a whole new phone when multi-tasking and in overall snappiness (app install times, loading times etc).