|Indeed, there are many uses for the diskless computer, if it has a CD-ROM drive.|
Knoppix, when combined with a USB flash drive, can make any diskless PC -- or a handy Windows box -- your personal Linux workstation.
Further, there are many genuinely useful Linux LiveCD's for firewalls, routers, gaming, thin clients, servers, development, penetration testing, benchmarking, and more. Virtually all of the following categories have several Live CD's competing with the one linked below.
Try some of these:
...anyone willing to fumble around in the GUI for half an hour, and throw out the occasional Google search shouldn't have too many problems using the Knoppix interface. The most recent version, Knoppix 3.9, comes with Firefox and OpenOffice.org 2.0 Beta, so if you're already using the Windows equivalent, Knoppix is that much easier to pick up. This still leaves the question, what can be done on a computer without a hard drive?