It could be used as a boot drive. It could be used in a netbook. For that matter my wife's laptop that is beyond a netbook probably doesn't have more than 30GB used on its hard drive.
Nevertheless we're still not there. It will be great when the 60GB class of drives gets close to $100 and the 128's are below $200. Lots of people could get by with 64 or 128 in a notebook, or even a desktop if the have alternate storage available. Even the high performance CAD workstation I'm using right now only has 57GB used on C:. Maybe they'll get there the second half of this year.