I used the PowerBook 100 from 1991 until its hard drive crashed in 2004.
The PowerBook 100 is perhaps my favourite Macintosh of all. It went with me everywhere, was used in legal work, for FileMaker development and for making notes and writing reports as an Australian delegate to various yachting rule maker conferences around the world.
It was replaced only when the hard drive crashed and the temptation of colour became too great to resist. Not bad after a decade and having circled the globe a dozen times.
Having previously worked in offices where DOS was the ruling operating system, I really liked the Apple philosophy about making the computers fit the people.
Apple seemed to take this literally with the amazingly small size of the PowerBook 100. This was partly achieved by separating the floppy drive into an external case, a clever trade-off to achieve the really handy compact size and one which surprisingly was not repeated again until Steve Jobs rejoined the company.
The RAM may seem tight today, but applications were so compact at the time that it was possible to run FileMaker and ClarisWorks simultaneously. The tiny hard drive also forced one to be very disciplined about what was carried aboard. Thus only current work would be loaded, which actually forced good habits. The hard drive also had the very useful feature of a forced spin down under system control. The end of the useful life of the PB100 only came with the need to connect to the internet and to view pages in colour on a larger screen.