SSDs are great, but not at the expense of other things.
When building a gaming machine you always want to make sure your system is good before buying what I call "rich man toys". This means if the average price of an SSD is around $100, make sure that $100 wouldn't be better spent somewhere else. If you need to drop down to an i3, or get the 650TI instead of the 660 then maybe you shouldn't get the SSD. If you need to go down to a 1600x900 monitor instead of 1920x1080, then skip the SSD. They are like sound cards and fancy keyboard/mice. Great to have, but don't buy at the expense of the rest of your rig.
If you have a 3570 and a GTX670, I fully support getting an SSD. I was thinking more for those who are running a 2120, GTX550, 4GBs ram, or other such things. I would also suggest getting an SSD over sound card or keyboard/mouse.
SSD's are fairly inexpensive now as well especially if you pick something up in the 64-128 gig range to run your OS and the games you run most off of, hell i picked up a 256 gig Agility 4 on black friday for $110 before the mail in rebate, 3 months ago i paid $160 for a 256 gig Samsung 830, total i have 768 gigs of SSD storage in my computer and i wouldn't dream of going back to standard drives for anything other than mass storage of movies/music
Should be fine. The question now becomes what do you put on it? Most like their OS on the SSD. I find hdds to be fast enough for me. I put my steam folder on my 128GB Samsung 470 so that I can get the faster load times. If/when I get a 256GB SSD I'll probably put my OS on my Samsung and Steam on the 256+. As mentioned above normal hdds are fine for storage of media files.
I bought a 60GB SSD for my C: drive and a 1TB for my D:. Put the OS on the SSD and installed all programs to the D:. After the fact I realize the D: was "green" and spins down on it's own! Noticeable lag in loading programs.