Like Chris, Wes have said. You don't put everything on it. Just programs that you really use, for me it's Vent, CoreTemp, Chrome, CCleaner, Fraps, MakeMKV and Malwarebytes, that is it. You don't need everything on there either.
I would suggest doing some research first, then you know what your getting into. What kind of speeds to you want. Sata2 or 3 and what kind of brand. Even if you bought the worst SSD on Newegg, its still WAY faster than a Raptor or any other mechanical HDD.
For instance, I have 3 80gb Intel X-25M's in 3 computers. The laptop has shown the biggest improvement. I gained an hour of battery life just switching to an SSD. The thing boots instantly, from off to windows in 12 seconds. The Shuttle will restart faster than your computer will shut down. It will load 50 apps as soon as it hits the desktop with no problem. From cold to Windows in 15 seconds. The big computer that I have is a bit different. It has a bunch of stuff to load when Windows starts. Vent, WHS console, CoreTemp, Chrome, EVGA precision, Steam, My logitech keyboard apps, my logitech headset app. There is just much more for it to do and it boots in 20 seconds from cold to Windows.
The other thing is this. When I say cold to Windows, that doesn't mean oh I have to wait to click on shit either. You click on it and boom its up. I can click on every single app on my desktop and boom their up and running. No waiting for stuff to load was the biggest payoff in my eye's.
Do what you want though. But I can easily say that I will NEVER build another system that doesn't have an SSD regardless of size and other drives for storage. You almost just need to use one with an SSD to see what we are talking about.
What really sucks is when you use it everyday it becomes slower, in your mind because you are use to it. Then you go use a friends PC and it just AWFUL. If really sets you back.
No better upgrade in my eyes then an SSD for overall performance.