When using glUniform1f() to set a float value on a uniform in a GLSL shader in Linux (Ubuntu 10.10), you get random values set. This has nothing to do with the driver per se, I got exactly the same behaviour under Mesa OGL on Intel as on the nvidia proprietary driver. It also works if you use GLEW to remap the calls.. so it is probably some header-file somewhere which is incorrectly defining or wrapping the glUniform* family of calls.
In either case, simply using glUniformfv() instead with a count of 1 and a pointer to the float variable you want to set, solves the problem.
Hope this helps someone else (I spent some hours searching for this bug
