MLC SSD have a limited life time, the vertex announced a MTBF (Mean Time Before Failure) of 1.5 million of hours. This number is only based on a statistic of “how many gig of data you’re writing everyday”.
So if you really want to know the percentage of the remaining life you can do it if you have the firmware 1.30 or newer.
Again, this procedure is taken from a post of the OCZ forum.
Download the free tool CrystalDiskInfo, install it and run: