Screenwriting machines and software
I am a big fan of grabbing the biggest screen available. 15" is swell by me. My thinking is that while I may be on a plane for a few hours, I am more likely to be working in a hotel room, or some other flat space. At that point, the screen is a lot more important to me than portability.
As to software. I use a legal pad (Levengers, Cornell lined) and a fountain pen when I need to really think about stuff. Once I know what I am doing I tend to write in Final Draft, MovieMagicScreenwriter 2000, or Slugline. I have had good luck with all of them. If I am working on a TV show, I use whatever the show is using. Because I have been doing it for a while, the software pretty quickly becomes invisible to me.
I will admit (this could have been posted by some else posing as me) that I have on occasion used Final Draft's excellent margin cheating abilities to get a script down to an acceptable length. It's always better to do the rewrite work initially, because once a script gets budgeted, you're going to have it there for all the world to see and you may not have the time to spend shortening it in the way that you really want.
One man's .02, YMMV, and all that.
Adam Rodman