If one should buy a laptop without having a desktop, Which of these screens is enough 12.1", 13.3", 14.1", 15.4"?<p>Consider the crick after carrying a 15.4" for hours!
I use a 12" Powerbook that I take everywhere. I have big displays on each coast that I plug it into when I'm there. I'm definitely more productive with the big displays, but I've worked for a month using just the laptop itself and it was acceptable. It may help to be using a very succinct language.
Resolution is the big differentiator. A Dell 24" LCD does 1920x1200. So does a 15.4" WUXGA laptop. I worship at the resolution shrine.<p>I've carried both 15" and 17" 1920x1200 laptops <i>everywhere</i> for years, including quite a bit of international travel. Even with a spare battery the weight never bothered me. I swear by 1920x1200 and prefer 15" to 17".<p>The other major consideration is virtual desktops. They're the resolution multiplier and help to make up for the lack of multiple physical screens. I use Linux with WindowMaker and half a dozen "Workspaces" dedicated to different tasks.
Find a way to have a desktop. Working for sustained periods on a laptop is asking for back and neck pain, fatigue, and probably long-term damage to your body.<p>Also get a good chair, and a desk that is the right height, while you're at it.<p>My lappy is a small 12.1", but I never use it for serious work--just email, and occasional "watching a movie with the girlfriend, but still have some work to do" time. I just got an OLPC XO (7" screen, I think) and plan to use it for my primary travel lappy...no temptation to work long hours on a lappy that small, and I consider that a good thing.
I have a 15.4" and it's suitable for travel. Though, I'm a huge fan of multiple screens / OS X Spaces (X alternatives).<p>There's just no way one screen without multiple screen emulation or external monitors will 'feel' right. Need more pixels!
I had tried a Dell 12.1" M1210, Macbook and Macbook Pro all before. To me the bigger the screen/resolution the better and Macbook Pro is certainly one of the lightest 15.4" so I would recommend that. Personally I could not tell the weight difference between carrying a 13" Macbook and 15" Macbook pro.<p>However, 13.3" and 1280x800 is my minimum requirement that mobility could not justify any smaller spec.
I would get the smallest laptop you can find with reasonable specs, and just get a 24" Dell (or 30" if you get one with a decent video card) display to hook it up to at your desk.<p>This is convenient because you can easily take it to meetings, vacations, etc. and have all your data, but most of the time you'll be hooked up to a big display and won't need to use the laptop as the primary screen.
I'm fine using a 12" Powerbook, but they don't make that anymore. My next laptop will probably be a 13" Macbook. <p>When it's hooked up to a 20" screen, I've got plenty of space. When I'm just using my laptop alone, I just use a multiple desktops app (like Leopard's spaces).