For my most important work, i.e. calculation, I'm using UNIX and Linux running on various systems. My laptop is a laptop, and it has no importance. I mean, it has to have a real keybord, a screen bigger than 13", and it should be thin and light, because I have it always with me (indeed, I have two of the same, because I don't want to lose one second, if one breaks). The flash memory is very useful, and I could not admit booting in more than some seconds now.