In a short answer, yes it is to start with. But in time, you will fill it up. I started with a 60gig SSD, and worked hard to make sure nothing else went on the drive. After about a year, I finally went and bought a 120gig SSD, and stopped spending so much time trying to keep stuff from going to it. After another year, I have about 65 gig on my boot drive. I still manage what goes onto it, I just don't nit pick about it as much.
There are other things than just the OS that benefit from the SSD.
I would suggest for a boot drive, a 120 gig minimum.
As time goes on, and SSD's get cheaper, I am thinking seriously about getting another larger SSD (500gig) that I can return to using as a boot/program/app drive, and resort to using my mechanical drive purely for data storage. Why? Simply because everything on that SSD is so much a pleasure to use. Its snappy and fast, and before long, when you use one for yourself, you will see what I am talking about.