How often were/are bayonets actually attached to rifles?

I know that almost every single issue-rifle in the last 150 years has been issued with a bayonet, even the G36, L85, and M16. But how often have the bayonets actually been attached during various points, specifically, WWI, WWII, cold-war, and modern-day? A lot of surplus rifles I see, including one I own, will only shoot straight to the sights by default with the bayonet actually on the rifle.