Motion is a relatively new company that makes only TabletPC slates.
I think folks are generally happy with them. Arguably, they are the best TabletPCs.
http://www.tabletpcbuzz.com/forum/forum.asp?FORUM_ID=25 (Motion Tablet PCs)
http://www.tabletpcbuzz.com/
If the apparent lack of a keyboard is bothering you, there are keyboard accessories
https://www.motioncomputing.com/store/Default.ASP?WCI=wiInventory&WCE=wtcategoryDetails&Category=Input%20DevicesLE
Note that TabletPCs run a extended version of Windows XP Pro... so it can run everything that an ordinary laptop can run.
I use a TabletPC because I lecture with it... if I had to upgrade (and had the funds to do so), I'd get that Motion or the new IBM/Lenovo ThinkPad X41 Tablet.
Considering your Sony link, it looks okay... but I guess it depends on what you want out of your laptop.
For me, 6.5 lbs is heavy. My tablet is about 3.5lbs. I need an easily portable machine, as opposed to a desktop replacement. Of course, I realize that this Sony has some on-board components like a DVDRW.
Certainly, this Sony is much faster and more powerful than my 2-year-old tablet. However, that new Motion LE1600 is comparable in speed.
Last year, my wife got a nice Vaio, the V505DX. The V505DX is small, weighs 4.3 lbs, and the battery lasts about 5 hours. Be warned, however. Check the battery life for the model you choose. A friend of hers got a different Vaio model (Z series, P4?) with a big screen, and it lasted only about 2 hours.