I've used VimWiki for a couple years now. I use the most basic features (Enter, Backspace). The ability to instantly jump to the wiki is the most useful (Leader W W). My wiki is just a folder in my Dropbox so I can get to it on almost any computer.

When I started, VimWiki syntax was better supported than markdown. I've seen lots of markdown related pull requests come through, so maybe that's changed.

I use VimWiki for:

  * Life goals (stretch and short term). I use it almost as a centering tool.
  * Poetry
  * Passages from books
  * Book summaries (that I write)
  * Lecture/Speech notes
  * Notes on misc. items I want to explore
  * Ideas for future science fiction short stories

Last summer I wrote a simple Awk script to extract VimWiki style definitions (Term::Definition) into TSV's for importing into Anki. I was frustrated that I couldn't fully automate this process without modifying Anki. Maybe someone else has figured this out?