It is usually pretty reliable, especially in the summer.
The 60% is sort of misleading.
What it means, by the definition from the NWS is: the likelihood of occurrence (expressed as a percentage) of a measurable amount of liquid precipitation . . . during a specified period of time at any given point in the forecast area
Or:
There is a 60% chance that measurable precipitation will fall at any point in the forecast area on the specified days.
The forecast areas that most news stations in Central Florida cover are pretty large. And they usually cover both the interior and coastal regions. The weather can be quite different between these regions.
That said, be prepared and have ponchos ready. Some of the best days I've had at WDW were in the rain.
Ted