No LAS has ever been used in flight. Gemini did not even have a LAS. It had ejection seats but the astronauts doubted that any ejection was survivable and did not use them even in an on-pad shutdown.
A LAS only saved one crew, on Soyuz, and in that case only because a fire was visible long before the explosion. If the fire had started a little earlier in the count ground personnel would have been killed, with or without the LAS. The Soyuz LAS also caused a fatal ground accident. No US rocket has ever simply burst into flames on the pad prior to launch. The only US crew lost during launch, Challenger, was almost a quarter century ago, and the failure mode was corrected.
The big problem I have is with people shooting from the hip and claiming that the LAS eliminates all or even any significant part of the risk. It helps only in a narrow spectrum of contingencies which are extremely rare. There are other risks in being an astronaut; at least six were killed in aircraft accidents, including Yuri Gargarin, the first man in space. It's more realistic to thoroughly test designs at the prototype stage and eliminate the failure modes. This is the approach Rutan is taking; his passengers will not have to wear parachutes or pressure suits. One of the astronauts was killed in a crash while simly riding as a passenger on an airliner; occasionally there is an airline crash that kills hundreds. The probable cause is identified, directives are issued, and people pack onto airliners of the same type within days, and without parachutes or escape rockets.
Most likely Dragon will be required to have a LAS, not because there is any actual failure data showing it is needed, but because the assessments of NASA "safety experts" are based on simply making a list of every major component, assuming that it will fail, without actually identifying the failure mode, and creating some "rescue" procedure that will, on paper at least, be followed if it does, thus magically eliminating all risk. If anyone with real training in reliability engineering thinks this is a legitimate strategy please speak up. Several astronauts were killed in aircraft that had ejection seats; how come they were not saved by the "escape" procedure?
At least the Dragon LAS can be much smaller than the Orion monster because the Falcon doesn't have obsolete solid fuel boosters, so the booster will shut down and not try to run over the capsule while it is separating, and the capsule itself is much lighter because it doesn't have to go to the Moon.