I have a Sony SZ270P which is the Core Duo version of the ones you link to with Core 2 Duo. I can't comment on the C series.

I like the SZ270, the screen is great, its light ( 3.73 lbs) pretty fast and the standard battery lasts 4-5 hours web surfing or Microsoft Office type stuff with WiFi or Cingular Edge turned on and using the integrated Intel video, not the Nvidia.. Only lasts around 2.5 hours playing DVD's. Sound volume is not nearly as loud as my old Toshiba M35-S320 or my wife's Toshiba M115-S30094. I have to use a Boostaroo to watch DVD's on a plane

I purchased the 3 yr accidental damage extended warranty from Sony which claims to provide on-site repair service. When the DVD drive made a loud noise when spinning and the cover plate of the DVD tray fell off, I had occasion to need service. Turns out that during the one year basic warranty you have to mail it in even if you paid for the 3 yr extended.
They sent me a flat cardboard that I had to fold myself into a box to send it in. It was fixed but in the process they removed the Cingular Edge Antenna and did not replace it, and they updated my BIOS and drivers which somehow made the Cingular card stop working once they had mailed me a new antenna causing me to have to reinstall the old stuff myself.

I had a better experiance with Toshiba when I drowned the M35 with Diet Pepsi. This is not a big sample but I was left with abad impression from my Sony support experiance.

With Reference to the Cingular Edge, it locks up now and then and I have to reboot to get it working again and its much slower than Verizon EVDO but I am happy to have something.

I would have considered the Panasonic Y5 if it had been available in my timeframe.