I booked a shuttle with San Juan Travel in Flores to go to Tikal. There were 5 tourists on the bus and the driver picked up a local. This was at about 8am in daylight. About 40k to Tikal we were stopped by masked and armed bandits. (at least 2 rifles, 1 pistol and a machette)
They made the driver drive into the forest off the road where the mini bus could not be seen. They proceeded to rob us. Luckily no one was hurt and thats what insurance is for! However the local the driver picked up dissapeared on an empty bus straight after that wouldn´t take us westerners. The Inguat offical (who was really helpful with the police and cancelling of cards etc) said the only reports of anything happening on that road were to San Juan shuttle buses.
If you want to see Tikal, pay for a full offical tour, rather than use San Juan for the shuttle and buy entrance seperatly. I beleive they are the only company to do shuttles. We did everything by the suppossed book. Recommended agency, daylight, carried limited stuff etc but it still happened so beware!