GLM 0.9.1 branch is finally reaching the status of stable with GLM 0.9.1.0.
From GLM 0.9.1 beta, mainly bugs has been fixed. GLM has evolved on many sides since GLM 0.9.0: Improved documentation (manual and doxygen), better test framework, simplified setup/options/configration of GLM and new experimental SIMD API.
GLM 0.9.1.0 is not 100% backward compatile with GLM 0.9.0.8 but mainly advanced usages should be affected by the differencies. Have a look at the GLM manual for more information on how to use GLM 0.9.1.