I have been using a PowerBook for the the past 4 years. I use it both at home and at work. I am used to the smaller screen. I don’t mind the keyboard, but can’t stand the trackpad. But a mouse is cheap.
Another full-time PowerBook user here. At work I plug in a nice 19 inch Trinitron and a Certified Original Apple® Extended ADB keyboard and a real mouse. (In fact, if I’m not in MacOS X, I run the 19 off of a CardBus video card, using the built-in TFT screen as a second monitor for an extended Desktop). The only time I’m reduced to the laptop’s screen, keyboad, and trackpad is when I’m mobile.
I’m constantly moving between my own apartment, my girlfriend’s apartment, and work, and with the PowerBook wherever I am, my computer is. None of this “oh, I left that file on the other computer”.
You do pay for it – laptops are undeniably more expense, and their PARTS are more expensive; and they do tend to require repair more often (on the other hand, your desktop or tower computer might not last quite so long if you lugged it around and plugged and unplugged all its cables twice a day either). But they are more upgradeable than people give them credit for (I bought mine with 128 MB RAM, an 8 gig drive, and a 300 MHz G3 processor; it now runs 512/60/500-G4 and has acquired a Zip drive module, CDROM module, and entry-level video digitizing card).
I think if you don’t go for the cheap knockoffs, you’ll find they are more durable than usually given credit for, too. Mine is a 98 model, a “WallStreet”, and therefore about 4.5 years old.