I have (and use) external hard drives, but it seems to violate some kind of "laptop" principle to be tethered to the desk. Backups, yes; general writing, no.
I use a 4Gb thumb drive for much of my writing. That allows me to travel with just my work laptop without synchronizing files. It also allows me to work with poor or no connectivity.
Today, I went to my local Apple Store to talk about a new MacBook Pro. The sales person had a bunch of ways to preserve my old machine by using removable hard drives and my Mobile Me account. After a long conversation I had to beg them to sell me a new computer. It appears that they'd rather preserve my investment than wring more money out of me.
What? Make do with "good enough"? Improve slightly to solve the actual problem I actually have? Spend the least to get the most? That seems downright un-American!
The sales person was pretty sure I didn't need a MacBook Pro. A MacBook was good enough. (I have a older FireWire video camera, so the Pro is necessary.)
And that's not all. The on-line purchases from http://store.apple.com/ allow more customization. In-store purchases do not have the same degree of customization. Since my needs were unique, the sales person sent me home empty-handed rather than sell me a product that's not exactly what I need. We went through the on-line ordering a few different ways to explore what I actually need.
It's odd to meet principled sales people.