I found that if you take a companion in the Reaper Lair and attack it, the Reaper will appear when your companion attacks you.
Very interesting, but what does it mean?Edit
It was kind of cool to see the Reaper, and the Lair had a good atmostphere. But the rest kind of fell on it's face.
I traveled around the Cairn for the better part of an hour looking for the dam shards, to what? Get a guy throw up on me once or twice before dying, a few soul gems and a Daedra heart? It all seems kind of, pointless. Alot of work for very little reward.