That's right. Even the iPhone4 was downclocked to 800Mhz from the 1GHz A4 which iPad2 uses. It's a matter of striking good balance between heat, battery life and performance. These mobile phone SoC's are made with much higher yield than what they actually are made to run at to ensure they are stable even while they are under a blazing summer heat with no air circulation. So it's even better than the desktop PC CPU's IMO.

Yes, I was the one running my N900 at 1.1GHz for both min/max. Heck, even Lehto (the first one ever to overclock the N900 at TMO afaik) told me he does this. But this isn't something I would recommend for everyone unless you know the risks. (possibility of instability, hand burning, exploding...just kidding...hehe..) But yeah, it should only be done if you are experimental and fearless.

BTW, I got my N900 replaced this week as my USB socket ripped out. (my kid stomped on the cable/n900 while it was still plugged in) This new one I have is even more stable than my previous one as my last one was quite unstable at 1.15GHz using ideal voltage. But this new one seems to be rock stable. My last one never skipped a beat at 1.1Ghz using xlv voltage. So this one should last me even longer maybe as long as my kid doesn't kick my N900.

I'm actually eagerly waiting for someone to overclock the N9.
I reckon 1.2GHz is just guaranteed and 1.4GHz is highly possible.
So yeah, bring it on. I'll risk my N9 for the community.

(AFAIK, I was the first person Lehto gave his custom kernel to to overclock the N900 other than his own)