I'm finding $300 Acer laptop (or netbook, one of their Inspire line) loaded with Linux surprisingly usable. (It was preloaded with Linpus, but I've replaced with my own.) At 1.10 GHz Dual-Core, 4GB RAM, it's a bit slow at times, but as long as I'm not running intensive process on it, it's very usable on the go machine. (Mainly, TeX, translations, web stuff, browsing, and occasional spreadsheet, is what I do on the machine.) I do have a desktop machine for things that requires more power.
Well, I did add that I do have a desktop that I use for more demanding tasks.
I guess it's the matter of doing the right thing on right machines.
Though, I do understand there are plenty of people out there who requires a laptop with decent capabilities. A $300 machine that "surprisingly usable" can be a good compromise in some use cases.
