Are you carrying two laptops at the same time? I found I've not had too much trouble carrying my laptop in a backpack since 2008 (when I replaced a beastly ~5kg 15" Acer with a thin 2.5kg 14" Dell Latitude).
That really made a huge difference (the Acer used to give me backaches, as it also had a much larger power brick) but all the laptops since didn't really bother me in terms of weight.
