A colleague and I recently updated to 8.28 from 8.27 and we both immediately noticed severe performance degradation, observed objectively in memory usage and subjectively in an almost entirely unresponsive UI. Both of us are using Grasshopper, only one of us has Python component. Both sketches are pretty small.
Rotating in the Rhino window will cause memory usage to jump to greater than 15 GB, though with time, memory occasionally drops as low as 8 GB.