Just curious since I haven't done freelancing yet... how do you determine what is billable vs. non-billable? If 60% of your time is billable then what constitutes the other 40%? I know part of it is looking for new work. What else?
Another big time sink (that I didn't realize) is all the work that's involved with even setting up a contract or freelance relationship. Depending on the client, you can spend weeks waiting / working out details before the project begins. This is why longer projects are more valuable (and can be billed at a lower rate) -- since there's always some fixed overhead per project.
Also, I will often not bill some hours for clients that have given me a lot of work over the years.
I spent years as a sysop of the CompuServe Computer Consultant's forum. I'm kind of familiar with this stuff. <g>