remember that for blending, you dont need a blend channel for the first texture you use, like say, dirt.. just blend on top of it. So you can have 5 terrain textures and only the RGBA blend map.
Or, do something more sophisticated than this simple and ugly blending...use perlin noise and multiple blending areas based on slope, height, etc.
These standard terrain shaders just fading smoothly between tiled textures look pretty bad.
