My friend owns an ARM9 based netbook (Sorry but I don't remember the model, it's probably around 3-4 years old now, I think it was just called "netbook" actually) and I own a MIPS based netbook (http://en.wikipedia.org/wiki/Skytone_Alpha-400). The newer skytone netbooks are already ARM based, and have been out for quite a while. My only two beefs with them are the default OS absolutely blows (it's easy to use, hard to modify or install ANYTHING, luckily you pretty much just need copy a tarball of the OS image you want to load onto it on a SD card to get a normal distro.) and the keyboard sucks. (though I've yet to see a netbook with a keyboard that didn't suck). I've seen a couple ARM based netbooks hanging around frys electronics the past few years as well, they're around just not pushed and advertised as hard as the x86 ones, and tend to only appear for a few months out of the year.
I recommend buying one as they become more common, the difference in battery life alone is worth it.