Risto Nykänen wrote me that Guatemala is going to observe DST from 2008-04-30 to 2008-09-29. Searching for confirmation, I found an article at http://www.prensalibre.com/pl/2008/enero/29/217165.html, apparently from a Guatemalan newspaper. It says:

"El Gobierno guatemalteco adelantará la hora oficial en a partir del 30 de abril en un intento por reducir la demanda de energía eléctrica.

“'Ya es un hecho, se va a cambiar a finales de abril para tener horario de verano', dijo el vocero presidencial Fernando Barillas.

"Con la medida el ejecutivo espera obtener un ahorro de 60 megavatios diarios entre el 30 de abril y el 30 de septiembre, cuando termine el horario especial. ..."

My translation:

"The Guatemalan government will advance official time starting on April 30 in an initiative to reduce demand for electrical energy.

"'It is already a done deed, we are going to change at the end of April to observe summer time', the presidential spokesman Fernando Barillas said.

"With this measure the executive hopes to save 60 megawatts a day between April 30 and September 30, when the special schedule ends."

Gwillim Law