I've often questioned this answer. It's my understanding after 100 years you have to give the property back to the landowner. Therefore, it's more of a lease.
The positive side of this is the permanent residency which will give you access to almost free health care. That with in itself is a big bonus. Now if you intend on living here a long time, you won't have to pay anymore rent after about 15-25 years except for the association costs to maintain the building.
The downside of purchasing property here is the poor standards of unskilled plumbers and electricians in this country. In addition, the water table problems which will affect the building. But, as in all hot beach front properties around the world, the water table affecting the structure is always a problem.
Because of the upscale boutiques there at the Pearl, I think it will uphold it's real estate value. I've heard from managers there that it's a playground for wealthy Qatari's and other gulf men. I guess the women will teach them how to spend their money!