Yeah, thats around what i shoot for 1.2kg-2kg. I currently have a 2kg machine, but as it is 2 years old, things have moved on a bit. You can now buy a 2kg Sony Vaio with a built in optical drive and 13.3" widescreen (1280x800), and plenty of power. I find my machine portable, although i would prefer 1.5kg (look at the sony T series). If you walk all the way to work then you should be looking at lightweight units, but if you drive, then 2kg is fine.
I dont know about other brands as i usually just buy used sony vaios at ebay, but you should get more bang for buck with toshiba, dell, or ibm. But then you'd be giving up some style
Have a look at the
www.sonystyle.co.uk site and they should showcase some of the nice new ones. Although im not sure if i would actually buy a sony new, i think i'll stick to ebay as they come pre-tested. I hear sony's repairs and customer support is pants