When using proc glm, is the modeling and interpretation for a MANOVA very different from ANOVA? For the sake of argument, let's just compare a 1-way ANOVA with 1 dependent vs a 1-way MANOVA with 2 dependents.
In other words, is MANOVA just a more efficient way to do ANOVA for multiple dependent vars, or is it a different technique that I'll have to get educated on?
It is a different procedure and generates a single test for the hypothesis that there is no effect on the combination of the two dependent variables. In the multivariate context, GLM also allows one to test multivariate linear combinations of the dependent variables, providing a different approach to repeated measures analyses than you would get in MIXED modeling.
As a side effect, it also does the two ANOVAs, with a caveat about missing values. GLM does listwise deletion, so you will get different ANOVA results if the dependent variables have different missing value patterns than you would get by running the GLM procedure once for each dependent variable.