3ghz is much easier to appreciate as being better than 2ghz.
Same with megapixels. If I got a camera/phone with 3 megapixels and you've got one with 12. One can assume (and 9 out of 10 times, you'd be right) that the 12 megapixel camera will have more bells and whistles than my lowly 3 megapixel version. That goes for lens, ccd quality, effects, lcd quality, etc....