We have one in the office. My boss taught me how to do it - took about a week as everyone else has said.

We do it when we're on long phone calls. It sounds like a distraction, but I find it actually helps me focus. It's just turning cubes from rote memory, paying slight attention to where things need to go. It's far less distracting than picking up the phone and firing up Twitter.

(I was 39 when I learned, FWIW. Recommended to anybody.)

Same here. I have one on my desk to solve whenever I find myself procrastinating out of anxiety. Not only does solving it quell the anxiety, it has helped me get better at detecting the anxious state before I get sucked into another, more distracting activity for relief.