I use 'singular they' because at some point 'one' started to connote pretentiousness. I don't see how Spivak pronouns solve that problem, but this off-topic sub-discussion has convinced me to go back to using 'one' (for disambiguation's sake).
Oh man I wish these were in widespread use. It would simplify things greatly for everyone. I kinda wish HN just started using them and it spread out from here.
There are a bunch of different proposed gender neutral pronouns... which is part of why no one particular set has caught on yet.