When I traveled I use to take just one laptop, before realizing why owning two was such a better idea. If you travel and the internet is your job, what happens when your sole source of work breaks? Do you cry and wait forever for your only laptop to get fixed?
A good reason to carry two laptops is simply, if one breaks, you have one on backup that will really help when traveling in countries where electronics are really expensive. I didn’t realize this until my laptop broke while traveling abroad. Now I know two eee pcs will be much better next time than risking having my laptop break again.
Even at home it can be useful to have two laptops. Even other things like extra power cords can really come in handy where you would least expect it.