Please don't spoil it
I have been a few times, i actually stayed there for 2 weeks in 2002. Awesome island, very frendly people, and very chilled. If you plan on going for a day then you will need transport when you get there. taxi's exist but are very expensive, car hire is pricey but you have freedom. Moped hire is best as cheap and easy (you can rent from la Savinas) push bikes are available but the island is not as small as you first think so you will be knackered. If you have no transport then you will only get to one beach.
The beaches are georgous and the water is clear, be prepared to encounter nudists on all beaches, dont gawp as you will be the odd one out if you wear clothes !!!
Illetes beach is my fave, followed by Mijorn. Yes Blue bar is cool but if you are only there for a day then you miss "Kaya's" sunset music and the parties afterwards.
If you go, have respect for the place. The beauty of the island is that due to strict planning laws, no more building can take place, it is what it is and will never suffer the high rise nightmare of Ibiza.
Hope that helps, i will be back there on 4th July, can't wait to get my kit off.