For several years now traffic is speed controlled as it exits transatlantic airspace, and over the continent to give it an arrival time at the holding point. This "linear holding" is more efficient and less polluting than a traditional holding pattern. It reduces the holding time in the traditional holding pattern, though at busy times these still get used and it is not unusual for an aircraft to have to take a quick spin round to fit in with the other traffic. The amount of traditional holding has noticeably decreased as a result. I'm sure one of the ATC contributors could flesh that out more.