I do. I use a nearly 3 year old Acer netbook, running Ubuntu. When I switched to Ubuntu I took out the stock 160 GB hard drive (with Windows XP on it) and installed a 320 GB drive. I use the Open Office suite. The nicest thing about Ubuntu (or other Linux distros) is the ability to switch among virtual screens -- that eases the difficulty of dealing with such a small screen.
The small screen is a bit of a challenge, but I've gotten used to it. I will admit that I (long ago) used to write on an Epson Geneva PX-8
with an 80 column by 8 line display (no descenders on lower case letters). The netbook is a huge step up from that. Still, I do use cut-and-paste more frequently with the netbook.
As far as writing "on the go" -- mostly, I use it in the house. I use it in the living room in the morning and in front on the TV at night. I have taken it out to a Barnes & Noble and our local library a few times and used their wi-fi, but not nearly as often as I thought I would.
I use the netbook every day and I'm very happy with it, but I won't automatically replace it with another netbook when the time comes. I do use the SD slot to transfer files, but I still miss a DVD/CD drive. I've found myself checking out 14 inch laptops lately. I'd say it's a toss-up right now as to which way I go.