I've never seen anyone actually use a sliderule, though I have been in stores where the shopkeeper used an abacus. They were really fast with it.
I seem to recall one of the recent world championships in mental arithmetic was won by a ten year old Indian girl who, while doing some extraordinarily complex calculations in her head was simultaneously wiggling her fingers in front of her. When asked, she said that she was using an imaginary abacus to keep track of her calculations.
Oh, and I used to OWN a sliderule. Yes, and use it -- although this was back in the mid 1970s before calculators hit the mainstream, when I was about 14. At about the same time, a few of us in maths class were being taught to program a typewriter-sized adding machine that printed onto paper (like till rolls) instead of actually displaying anything.
Sliderules and log tables... all that work learning to use them, now atrophied and dead, pretty much along with the pocket calculators that replaced them.
(My first good pocket calculator was a TI-57. Programmable, but it didn't retain the programs when you switched it off. I got quite adept at writing little programs to do iterative calculations with it -- and I have a vague suspicion that I might still have it, somewhere...)
(Oh, and my first programming language was FORTRAN/4. Write onto 80-column coding sheets, send them off somewhere to be punched onto cards -- which helpfully had the code printed along the top of the card, which was useful if you'd forgotten to number them before demonstrating a cascade sort
-- and run, then debug and return the cards... the write/debug/rewrite cycle was about three days, because the computer centre we were using was 30 miles away from my school. And yes, I've forgotten it all too!)