I'll have to look through that onebag site, looks interesting.
I recently flew down to Florida with my fiancee and we each had 2 carry-ons (one camera bag, one laptop bag), plus a piece of checked luggage. After that experience I will never travel with anything more than 1 carry-on. I might still have to have an additional camera bag but I will make sure it's small.
I couldn't believe what people considered carry-ons! Some of them were huge. If you boarded near the end there was no overhead bins left and once or twice had to check one of my carry-ons. What's more valuable/breakable? laptop or camera?