It might have been my imagination, but there seemed to be quite a few more 29ers at the last round of the Thetford Winter series than usual. Still massively outnumbered by 26ers.
They definitely roll better and get through mud more reliably. I think the stuff about being slow through twisty stuff is, at least for me, not relevant, since in my case the limiting factor is how slowly my dullard brain works.
EDIT: even with my slow old brain and allegedly slow 29er steering I was still finding I’d be catching up riders on 26″ wheels on the fast cornery twisty bits.
My 26″ 456 is still a lot of fun though.