Everybody's working for the weekend!

My new job is going pretty well. There are times now in the day where I don't have anything to do. I feel kind of bad but when I go to ask for something to do my boss just names something we will have to do later, and I just go back to my room. Then he will come in the next day and give me a whole days worth of stuff to do. I was looking at the billing we give our clients for what I do, and even if I only spend 40% of my work week billable, I still make the company (in one week) what I get in my bimonthly check. Now this doesn't mean I am just gonna slack off!