As Joeteoh99 stated, OS and Skyrim are definately SSD material, so long as you have room. Putting the OS on a SSD made my computer feel like a whole new machine with how responsive it is and amazing boot times (less than 30 seconds to reboot and get back into windows again!). If you have a SSD and not put the OS on it you are missing out on one of the primary reasons the drives exist, do it, quickly, there's no time!
Skyrim, especially if you have a lot of mods installed, really likes the SSD too, fairly seamless transistion into dungeons/houses and loading new areas dosen't make the game stutter (maybe for a quarter of a second on my system).