Desmonds still got the ability...

[Reno]

He wanted Chlaire and her kid to move away from that spot becuase he knew that lighting was going to hit them. Since they didnt move, his last resort was to make a lightning rod, of course, lighting did hit it, and, I belive, this fianlly convinced him that he CAN see events.

[Jarlaxle]

That explains why he did it. I wonder if either Locke or Eko have simiar abilites, I would beleive that Lockes vision could be part of his ability. As for Eko, only time will tell.