Fan Fiction is a hugly popular pastime and the fact the authors can easily convert their work into PDF's for others to download and enjoy while still partially protecting their own copyright is what makes it the number one format in Fan Fiction.
It wasn't an issue with the Sony readers, but with the Kindle we have to convert them in Calibre first. If it wasn't for Calibre i would still have a Sony reader, Calibre was the only application that made me switching to a Kindle possible.
Giving the Kindle PDF reflow is quite a big deal for me and other Fan Fiction readers. It may be the format most people hate but it is a very important format.
If you don't know (and want to know) what Fan Fiction is go here
www.fanfiction.net