I've been under the impression that you need at least 300dpi on a desktop. My ultimate is to make reading a computer screen as easy as reading a high quality magazine. Most desktop screens are around 100dpi these days. A good computer print out is 600dpi.
Obviously handhelds need a higher dpi because their screens are smaller thus text needs to be clear to read it so small. Raph is presenting an article on the subject in Jan.
I'm interested to see his reasoning.