This is a mini-review to answer a couple of those questions:
I got the 1.8GHz and 1GB RAM, and so far everything has been extremely speedy. When you're not on AC power, it'll be 600 MHz either way, I guess. I don't see the point of getting the 2.0GHz on this machine. It's not for gaming, so what would you need it for that 1.8 or 1.6 won't provide? I think 1.8 is the right price/performance, and 1.6 if you want to save a few bucks.
If you're only going to get one battery, GET THE EXTENDED! I got the 4-cell as an extra, which seems to be all it's good for. I think 2hrs reg./5hrs ext. is probably accurate under normal usage (no dvds or games). Both batteries are a bit loose when they're connected. But I have carried it under my arm with the battery in my palm and it doesn't feel like it's going to snap off or anything. There is a groove in the 8-cell for your fingers to hang on to when you carry it like that. It's really a small difference, though.
The computer itself is pretty tiny, and pretty light. It might look big due to the angle of the pictures. It's much more compact than the 8600s I've seen and my mom's Acer 4001.
The screen is probably the biggest selling point, with the under-sized keyboard being the biggest drawback.