You don't need to spin down laptop HDD, you can dropkick a modern laptop without doing any damage to the HDD. Also 6 hours of battery life is fairly normal for non gaming laptops these days.
I think Netbooks are a solid replacement for a PDA if it's with you, but IMO they tend to be a poor compromise between a primary machine a portable one. They don't fit in my pockets and if I have a bag I only really care about weight at that point. I always have a cellphone that works as a PDA, if I am going to get stuff done I want decent keyboard, a high resolution screen, a fair amount of ram, and a HDD large enough that I don't have to care about what I am storing.
PS: Many "normal people" tend to have a web browser (word processor etc) and a IM client open at the same time so Netbooks resolution is still a fairly large sacrifice for most normal people. I use a 15" laptop with a 1920 x 1200 screen and it's great, I could drop down to 1680 x 1050 but that's low IMO.