It will reduce load times in games, as stated by people before, and you will notice a RIDICULOUS performance boost on your PC. It will boot up much faster, apps will open up faster and work faster, and your read and write speeds will have a good noticeable boost as well. So if you can afford one, I would DEFINITELY go with an SSD, I could even recommend you one, it's a samsung 128GB SSD, but if you want you could go with a lower or higher capacity SSD, that's the optimal I would recommend you.
Just the SSD: http://www.newegg.com/Product/Product.aspx?Item=N82E16820147192
(Get this one fast if you decide to go with an SSD, because you'll get the new Assasin's Creed III FOR FREE!)
SSD w/ desktop upgrade kit: http://www.newegg.com/Product/Product.aspx?Item=N82E16820147134
(has a small shipping charge, and the desktop kit comes with a 3.5" to 2.5" drive bay adapter, in case your case doesn't have one built in or if it doesn't come with one. If it does, then go with the SSD above this one)