Okay to use SSD as only Drive?

It's fine, and many people do. If it's big enough to accommodate your storage needs, you don't need an HDD. It's just a cost effective way of having bulk storage for folks that have tons of stuff in their drives, but having SSD speed for their OS and applications.
 
So the SSD lifespan concerns that people talk about and the failing drives shouldn't be a concern?

 
Normal workstation use is 10-20GB writes per day. For a quality SSD, like a Samsung 840 EVO, that's going to work out to something like 14-28 years of rated lifespan. If you really abuse it, you might shorten it to 7-10 years.

 
Thanks for the quick answers. I was actually about to purchase the 840 EVO before posting this question. I just got hungup on reading different things about the best way to setup a system. I think I'll pull the trigger now on the purchase of the 500gb SSD with piece of mind.
 
Sounds good. You'll still need to back your drive up, as you would with an HDD, as an SSD is not bullet-proof - it's subject to some of the same hazards as a regular spinning disk, like power surges, driver and firmware glitches, etc. There are no guarantees against failure, only warranties. Odds are long in favor of you moving on to your next PC and drive setup before you wear out a modern SSD through normal use.