Ok first off kudos to you on such a KICK @$$ plugin!
The only other plugin I've found almost as useful is the aforementioned Cover Generator (it's fun to download fonts matching the series to make a halfway decent lookin book cover)
I was a little confused for a bit because, while looking up references to your plugin, I hit upon this site :
http://www.fanfictiondownloader.net/ and thought you had made this program and couldn't understand why the calibre plugin didn't have as much features.
I realise now that's not the case but I don't know if you want to get into contact with that author to see if he/they are willing to share info on how they do things. For now I only use it to grab fics from sites you don't support (mostly pervy/adult oriented fic sites
) but it leaves a lot to be desired in regards to metadata crawling and toc generation. Yours is FAR superior in those areas and also includes the story update function which is a godsend.
My only possible suggestion would be to add support for more sites even without full functionality i.e. toc or metadata. I personally would not mind basic support for the oddball site at least just to grab a fic in its entirety without having to depend on an autopager or worse CTRL+C/V.
Keep up the good work and hope to see lots more in the future...