In summer there are about 6 a day. Hydrofoils depart from Rafina, a short bus ride from Athens, once a day, take 4-5 hr., and cost 8,300 dr. Ios Ios has been taken over by youth, especially in the summer. It is the party island to end all party islands. There are also private resorts removed from the main town that enable the better heeled to enjoy the beauty of this wonderful island without the feeling imparted by the main towns visiting revelers.
Spring is the best time to enjoy the islands 'normality'.
I'd go back in a minute if I had brain cells to spare.