see the computer threads above for OneNote thoughs.Also, i can name at least three laptops that are under 3 lbs. the difference in three lbs of weight carried all day isn't trivial.
the X1 from dell, the R200 from Toshiba, and Sony Viao Tx.There are others. I recommend doing organized searches on http://www.cnet.com and http://www.notebookreview.com. Both of those sites should help. Also, see other review threads. Oingo has some great things to say about the X41 tablet, which I am also very interested in, and it weighs only 3.5 lbs.
I see "under 6 lbs." and see "a brick of lead." I'm only about the "under 4 lbs." group.