I'm quite surprised to see nobody has yet recommended an Acer Aspire One for this use case. I got my first AAO in 2008, when they were still little crappy 9", 1024x600 screens, and when the keys were actualy not at a standard distance. From the period when "Netbook" was being defined. It was far from perfect, but I loved it. Back then, I also had a 12" Dell XPS, wayyyyy heavier and bulkier, but of course, terribly more powerful. I took the AAO with me to way more places than the Dell.
Five years later, it was time for an upgrade. I got a new AAO; its models by 2013 had improved to a 10" 1366x768 screen, full-sized keyboard, but kept basically the same weight (the computers are quite thinner than the older generation).
I have recommended and bought seven such computers for friends and family. Never regretted it. As the original poster says, I'm after portability much more than power-- And having a US$300 computer that travels with me... Is just great.
Of course, I never had a hiccup recognizing all of its modest hardware with Linux.