My understanding (I saw it in here somewhere) that SSD will outlast an HDD, due to lack of mechanical/moving parts. I found this quote on a manufacter website: "100+ Year Life Expectancy (MTBF)"
Now, SSD do deteriorate due to multiple WRITES. But once the OS and Programs are installed, reads in really all the drive will do (but it's not that simple).
So, the trend right now, is to get a SSD just larger enough for the OS and Programs you want/need, and keep all your data/media/storage/backups on a seperate large HDD.
My OS SSD only uses 21.4GB of the 80GB available, but I have 1TB for data/media (My Documents, Music, Pictures, Videos, Downloads) and the pagefile, and a 1TB for backups. See my signature below.