I think someone would notice a several mile wide bubble sitting in the middle of the ocean. I think we have to think outside the box here, take what the producers have said that it isn't, and look for clues within the show as to the location of the island.
1. Aldo is reading 'A brief history of time"
2. Hurley says to Sayid the song could be from any time.
3 They moved Lost from 9 to 10, a new time.
coincidence, i think not