As Mr-T has stated, SSDs have their ups and downs.
1. If they fail, they will fail and you lost everything.
2. They are expensive.
The big question I would ask is what are you looking to improve. SSD are awesome for reading and writing at unmeasurable speeds. Sadly enough, since they are just memory DIMMS designed for storage, the bottle neck with the data flow on an SSD is usually the front bus.
Now if you do alot of rendering, opening and saving large amount of data, then you are not going to do any better then an SSD.
Besides that, SSDs are really not going to help you out with like gaming. Your game is going to start faster, but not perform better. Your system will start faster, but thats about it.
In my personal system, I have a 300GB SSD for my OS drive. I do my major data flow through there, OS, images, main programs. Then I have a 1.5 TB for a storage drive(secondary). This is where I put my 2 priority programs, like steam, origin, GIMP, Microsoft programs, etc.
On top of that I have a 7TB storage server. This is where I store all my music, pictures and movies.
Simply put it all depends on what you do with your system.