I run dunlop KR mediums and generally get one race weekend + one trackday. I know a couple guys who don't race that use them for trackdays only and get 4 trackdays out of them. It really depends on a lot of factors like track conditions and your riding style.
I will say that they are fantastic. That said, they are an expensive toy so consider whether they are a necessity. The grip isn't *that* much better than DOTs.