How often does bad turbulence occur in flights? on how many of your flights has it occured?

On most domestic services you won't find there's too much turbulence, and I think they have improved somewhat. Don't know if they're building planes better to withstand turbulence better, but my flights these days seem a lot smoother than they used to be. Occasionally while taking off you might feel a slight shudder or two, but flying on reliable airlines, it's unlikely you'll encounter anything of great worry.