I did the same trade (went from a 1.67Ghz PB to this MB) and I absolutely *love* it. My 1.67 wasn't slow by any means, so the speed factor hasn't really come into play too much, although I do notice a difference. I like the keyboard - didn't take me any time at all to get used to it. I really like the size.. I'm a student and this is much more portable, but with the same resolution so I often forget I'm even looking at a smaller screen. I do, however, have it hooked up to a 19" LCD for more workspace when I need it. I think I'm planning on 'upgrading' to a black one, though (selling this one and just paying the difference) because the white scratches pretty easily - granted, they're just microscratches, but still. Also, going from the aluminum "pro" look to the white plastic is kind of a let down.. I think the black would be a better trade, but that's just my opinion.
Hope this helps some!