I just traveled to Europe with an 11" MacBook Air. What a joy! After an older heavy 13" MacBook (also changed from my Pentax DSLR to a smaller, lighter but semi-pro friendly camera) my bag carrying shoulder is in great shape and ready to take on anything.
Although I have the the 128 GB option, I do have software that needs a larger HD. No Problem, I just cloned the HD onto a Western Digital external USB drive and run it all off that - yes it is a little slower, but nothing like as slow as I expected.
Now a Mac Air will be a routine part of my travel gear.