I've did this (alone) for a while. The things I discovered:

* Mosquitoes really, really suck the fun and productivity out of sitting on a tropical beach coding. * To a lesser extent, so does sunburn. * Finding somewhere comfortable to sit in shade is crucial, and harder than you'd think, and lying is out (appealing though it may be). * The ideal place to work was a beachside bar, without standing pools of water close by (attracting mosquitoes), that was quiet, serving coffee and wifi. Often hard to find, though. * Lack of wifi was sometimes a plus, provided it was never too far away. It's easier to focus on coding without Internet access.

In the end, my favorite tropical location to write code in was Singapore. The beach is overrated :)