It would depend on how you would use it.
My husband has had several PDA's. He loves them because of their fast on/off, they'll run Power Point and their tiny size. We've been looking at the Eee for a couple of months, and see it as an "inbetween" machine for a PDA and full laptop.
He's maxed out the capabilities of his PDA. New memory cards can help only so much.
With only 2GB of (flash) disk and no CD/DVD drive, it seems to fill a niche of “big PDA” more than laptop. Still, quite useful in that niche if most of what you’re using it for is web surfing and taking notes
I would consider the long haul anything where I actually have to be looking at the screen for more than an hour. This would be fine for plugging into a projector or quick 5 to 10 minute things, but anything that would be actual computer work is out. When I was younger and could read the small print on medicine bottles without effort sure, but like Steely Dan says, those days are gone forever. I now consider 14” to be a minimum useful screen size.