AMD vs. Intel. How important is the difference in clock speed?

If I remember right, years ago, amd would have a slower clock speed than intel but still run at an equal or very close to equal speed. Now I just don't get it. Years ago, in 2008 I believe, Intel had, or announced a 4ghz cpu. The pentium 4 extreme. Now most of the newer top end clock speeds are around 3.5. Has some focus come off of the clock speeds and shifted to other points of cpu architecture? Is an amd cpu with a slower clock speed still a rival to an intel with a higher one? I know other points such as caches, FSB, hypertransport/threading, blah blah blah. But how do I compare cpus now, especially between amd and intel. I miss the day when you could see a 600mhz cpu and an 850mhz cpu and just be like "I want that one!" hehe. Could anyone get me up to date here? Lastly, the manufacturing tech. What exactly is that. Is it the smaller the number is the cooler the chip runs? (45nm vs. 65nm) What exactly is smaller? Thankyou to anyone who reads through this mess :P