I've run a cheap 40gb Intel SSD for 2 years with no issues. I've converted that same drive over to a windows machine which is now running pfsense virtual on vmware and there are still no issues.
I'm guessing a large part is due to the size. The larger the SSD the more spare to have as reserve, the and less chance all the memory will be written over too many times to wear it out.
SSD drives are getting cheaper all the time. I originally only did it as the mechanical drive was noisy, as the ssd made the machine quiet. The windows machine was more important, as I wanted a quick windows/virtual pfsense boot time. Virtual also gave me easier backup/restore ability.