I would suggest going with the S series instead of the FS. I just made the same decision myself when I decided on a S460 over the FS "equivalent." While it was nice that the FS I was looking at had a TV tuner built in on a dongle along with PVR (Tivo-like) software for recording TV shows on a schedule, the small size and great battery life of the S simply beat out the few additional perks that the FS series had. I was replacing a monster of an HP laptop with this Sony - the battery life on my old HP was 50 minutes if I was lucky - and I've been VERY happy with the S series Vaio.
One other condition I had on the laptop was that it fit in my backpack-sized case so I can carry the computer with me to classes at the university I attend. The FS series was just too wide for it to fit properly, though it was thinner and lighter than my old HP, which fit the case fine.
I guess the bottom line recommendation I have for you - if you plan to use it 95% of the time in the exact same place and move it maybe once every week or once every other week, get the FS. If you will be taking it on the go on a daily or semi-daily basis, get the S.