According to the OpenGLES spec all implementations are guaranteed to support at least 128 elements in a uniform vector array:
MAX VERTEX UNIFORM VECTORS  128 GetIntegerv
http://www.khronos.org/registry/gles...pec_2.0.24.pdf

How does that translate to Mat4's? Is a Mat4 considered a kind of vector (like a 16-dimensional vector) or should you divide 128 by four to get the max number of elements in a Mat4 uniform array?