According to this:
http://www.storagesearch.com/ssdmyths-endurance.html

It doesn't seem to be an issue... all mechanical disks would have failed many times before any solid state disks (based on flash memory) would show any fatigue...

That is: The flash itself is not wearing out. Of course if there is any design fault in SD interface itself that just can not cope with high I/O... that's another story?