Travel and work: sometimes compatible, sometimes not.
Balance. (A good coffee, croissant au beurre and a killer view can tide you over an intensive project. Tried and true.)
On their blog Signal vs. Noise, 37signals wrote about empathy here and here. (The comments on the second post are also worth reading.) Interacting with clients is a necessary aspect of independent contracting. Empathy is a skill—37signals describes it as such, to which I wholeheartedly agree—and learning it, and using it, is crucial to client relationships. Graphic design is a service-based industry, after all….