The subdistrict municipality Ko Samui (เทศบาลตำบลเกาะสมุย) wants to become a city soon. It already has passed the population threshold needed to become a city (thesaban nakhon) instead of a town (thesaban mueang) of 50,000, although just barely. The necessary tax income to perform the duties of a city should be no problem thanks to the many tourists coming to the island. However I wonder what is about the third precondition for both town and city - a population density of at least 3000 per square kilometer. Since 1981 the whole island was covered by the sanitary district (sukhaphiban), the precursor of the subdistrict municipality created in 1999. But with a total area of 228.7 km² and 50,880 people as of December 2007 the population density would be just 222/km². The Thai article titled "Ko Samui ready to become a city" seems not to mention it at all.
And if I read this article from the Siam Rat newspaper the upgrade to city already happened on February 23, so for this one I would have noticed the upgrade on time, and not when it was finally published in the Royal Gazette months later. But it was really more fluke than anything else - I was browsing for blogs about Thai municipality, came across a posting in a German forum, and then just for fun tried a Google search for เทศบาลนครเกาะสมุย which surprising gave just one page of hits, and all relevant.