I was there with dollaroff a few days ago and I'll throw in my two cents. I've been to Barcelona, Sitges, and the Costa Brava many, many times. This was my first time in Ibiza. To me, it had aspects of both Sitges and the country around BCN. It's really the clubs which make it different from anywhere else. Clubs which hold 10,000 people and have a $70 admission!
Though there were gay people, and a smallish gay street in the town, it didn't strike me as particularly gay. And a local told me that it's billed as a 'family' destination with clubs for those who want them. I'm not really into the club thing so I probably won't go back. I'm glad I can say I've been there though.
August is probably the ultimate time to go since all of Europe is off the entire month...