Don't worry - it is not you! There are definite problems in the rendering area and indications are that the programmers are working on the issues, so hopefully they should be solved soon. I suspect that some of the widely differing results are actually caused by Material settings (shininess / emissiveness / transparency) and using materials that are "not designed for this element" (as we are warned) could be introducing lighting issues. I have found that sometimes restoring materials to their default settings solves an odd lighting issue.
Dispite all that and regardless of any forthcoming patch, I think Doug's Test file idea is a good one. Version 4 I think it was of FloorPlan, had a sort-of render test file. It was ideal for checking the processor speed of your PC. (Related - see my post on RAM Requirements in Looking For Help)