13" for the road - 22" on the desk!
IMHO here's my perspective. I use a 13" MBP as my single computer. I have a 22" external monitor at home and also one in my office. The latest 13" unibody MPS are solid and easier to travel with (one pound less) than the 15" (which I've been using variouse interations of MBs for the past 4-6 years) - plus the difference in price between the 13" and the 15" covers the cost of one 22" (I have Samsung and Dell externals; think I like the dell a little better) and an external keyboard/mouse. So I have the best of both worlds - a smaller easily transportable MBP, plus much larger video real estate when I'm "stationary" my office desk(s) where I do most of my long term computer work. So the 13" MBP "on the road" is easily tolerable to me. It goes with out saying, make sure you have an exernal hard disk at home and use a back up program.