History
The island's earliest inhabitants were probably some Pelasgian tribe, since almost all islands beginning with an "I" usually have such origins. In the 2nd millennium the Minoans were most likely here, and in the 8th century the Dorians got a foothold on the island. Local tradition has it that Homer died here, and the remains of his tomb can still be seen. The Venetians ruled the island in the 13th to 17th century with Naxos as the capital of the Dutchy. The Turks then invaded, and Ios was not liberated until the 19th century. In the 1960's the island was discovered by hippies from all over the world, and their influence is the origin of the island's reputation today as a laid-back anything goes party island.
What to See
The island's pride is the tomb of Homer, which basically is just a pile of stones. It is difficult to find, but if you manage to locate it it does tickle the fantasy. Local legend has it that he wanted to be buried on Ios since his mother was from here. There are a few interesting churches on the island as well, but most visitors like to go to the monastery of St. John (Ag Ioannis).
What to Do
Well, apart from the obvious, partying, there is always watersports, snorkelling, diving, beachvolley etc. Anything to do with beachlife.
Beaches
There are quite a few beaches and coves to explore on charter. Most popular are Mylopotas beach, Yialos and Koubaras, where many go skinny dipping.
Nightlife
Ios is overcrowded with bars and clubs, and the rhythm is high all through the night. Most places are in Chora, but there are also beachparties going on.
Food
On Ios grapes are grown, so you should try some of the local wine in the attractive tavernas in the old town. Other-wise you can get international food as well as Greek. Beware of the too touristy looking taverns though since the quality is not always the best.