Invigorating, that is, when it involves getting things accomplished. Today, since about eleven o'clock, I have worked on just two things - a group project and a research paper. Since that time, I have helped the group make great progress on the project, and have made considerable progress myself on the research paper. That's not even including the stuff I'm going to do tonight! This is probably the busiest day I've had for awhile, and for once I'm not yawning the whole day, but instead am finishing stuff that has to get done quick, and not dillydallying too much on the way. :-)