This really struck a chord with me. I always feel really awkward billing for an hour or two - either because it was no sweat to help them out because I wasn't doing anything anyway, and it was barely any work (a phone discussion and changing a couple of lines of code), OR because dropping everything to put out their fire pretty much hosed most of my day.

Just billing a full day once I determine what they need isn't trivial would have a nice effect on both my guilt and bitterness in these situations.