Hello, Owing to a back problem, I can't sit for long at a desk. I'm using my 8 year-old white iBook on one of those dinner trays .. the ones with the thousands of syrofoam beads in the underbelly. This is a very comfortable set up. Now, I'm thinking of graduating to the 17 inch MBP. My question is for those people who actually use the 17 inch on their lap... Are you able to work away for hours at a time, or is the machine just too darned heavy for long work periods? Yup, I could go for the 15 inch glossy, but the 17 inch offers many advantages Tray recommendations are welcome. Many thanks.