Well we all know, there is no right or wrong attire!
Personally & I mean personally:
Day Swimwear + Vest, T-Shirt or nice Shirt
Beach Bar Ushuaia or like: Polo & Linen trousers or tailored shorts.
Evening: I wear designer polo or shirts, with jeans.
I dress in nice clothes cause going out in Ibiza only happens once a year for me or 7/14 days. You can get away with swim shorts and a vest in most places but I can wear that on a trip to Tesco lol.
i'm in IBIZA Bitch

so I make an effort. Quite a few women in the clubs make an effort sexy shoes, nice dresses & Hair & make up all done, so I feel I should make an effort too as it's 2012 metro sexual etc etc not 1975!
But that's just me my motto is "dress to impress"! 8)