From my experience, reading and opinion, I'd say an SSD is more reliable than a mechanical device. A mechanical hard drive is just that - mechanical, and all mechanical devices are subject to wear and tear. The internal disk platters revolve at a high speed whilst the read head is constantly jumping backwards and forwards to locate data. That not only induces wear, it takes time.
An SSD just changes the state of silicon between 0 & 1. Figure it out.
However, SSD drives won't last forever, there's only so many times you can switch electrons from positive to negative and back again before they too will fail.
It's my opinion that the reliability of hard drives is pure pot luck, it does not depend on brand but of quality of construction, in other words - where it's made. And all hard disk manufacturers use a series of factories.. A month ago I had two Samsung hard drives fail on me, a 250Gb 10 year old device and a 4 year old 320Gb disk. I also still have a perfectly functioning IBM Deskstar from 1998 which almost defies logic. Granted, it hasn't been used for at least six years but I still think that's quite remarkable.
As Ian said, you could have a pair of 120Gb SSD's in a RAID 1, pricey perhaps, but peace of mind. However, that will only guarantee the recovery of a failed disk, it obviously won't protect against a corrupt OS.
I've been running my machine << see specs, for around 18 months now with Windows 7 on an SSD and a series of mechanical disks for data. See attached pic for my setup, disk titlkes are, I think, self-explanatory.
When buying an SSD go for the ones with the faster speed, they cost a little more but they're worth it.
EDIT/PS: I also use Acronis True Image to back up the OS to a storage disk, it's saved my bacon a few times, that's for sure. And I've now attached the pic