With a Salt Chlorine Generator, you should normally get 3-5 years on a pool that's opened 12 months of the year. For seasonal pools, you can just about double that time frame.
Although a salt system is "only" making chlorine on site, it is a great time savings and convenience item. The method in which it makes chlorine also controls Chloramines, which is more noticable with indoor pool environments. You will still need to test your water chemistry to ensure you're maintaining proper levels and balanced water (according to the saturation index).