Anand over at Anantech.com has spent a lot of time in the past few years analysing SSD endurance and does the math for us. Here is a recent link of a SSD review that includes endurance information.http://www.anandtech.com/show/5734/kingston-hyperx-3k-240gb-ssd-review
In his math you will see that he uses the estimate of 10GB of data written to the SSD per day (which is already on the high side). Now lets consider the amount of data FAH uses. Looking at my 'work' directory, the GPU folders are about 0.5 to 1MB and the SMP folder is about 5MB. So on my particular system(3 GPUs and SMP), I will fold about 4.6 SMP WU and roughly 26 GPU WU per day(using my TPF for the calculations). So that is about 49MB of data per day. Compared to the initial 10GB, this is very small. Running through the rest of Anand's calculation, we see that for the worst drive listed (think budget bin) with 3k write cycles with an original lifespan of 8.21 year the new lifespan will be 8.18 years or 2 weeks shorter. Better drives with 5k write cycles will last 13.7 years without FAH and 13.4 years with FAH. (5 minutes with a spread sheet and you can play with all the numbers for yourself
Now perhaps FAH is writing to the log file many times per day and perhaps it has other housekeeping disk IO, but they become smaller and smaller (and also harder to quantify). Even multiplying these small numbers many times will not make an appreciable difference on the lifespan of your SSD.
Of course this is just theoretical but I have only been running FAH on SSDs for less than a year, so can't offer any experimental results... other than having no problems to date. Considering how many GPUs I've burnt out, I'm not worried about SSD endurance.
In summary I don't think FAH is writing enough data to noticeably effect your SSD endurance.
edit: remember the above math is done using a 100GB drive, a 200GB drive would double the life of the drive given the same data use...