Koh Tao (turtle island) was only settled in 1940, and then as a prison colony. Starting in the late 70's it became a center for dive instruction. Now it is pretty touristy. While much of the island is pretty wild, the populated areas seem to be popular with the european, dreadlocked college set. Luckily, our hotel was way up the hill away from the party area.
We'd come to do some scuba diving, but after snorkling, decided it was too much of a hassle. The water's clarity wasn't great, and it didn't seem as if we'd have that much depth to work with. We felt we'd see just as much snorkling. Also, diving would be a whole-day endeavor with 30 people on the boat. If we'd had a chance to see a whale shark, I might have been more inclined to go, but none of the dives on our days were in the whale shark area.