We decided to nail down a few nasty issues and release another beta before running off to WWDC next week; as always you can read about said changes at the historical release notes page or the beta download page, and what follows is a brief summation.
We've addressed a couple of issues that popped up in the previous 5.2 beta 4 release, one relating to changes we made to dragging layers between canvases and shared layers, the other a repeating crash when attempting to inspect the drawing tools. Add to that some other bugs fixed concerning canvases and another crash when dragging objects from stencils, and that about sums it up.
OmniGraffle 5.2 beta 5 download page
Historical release notes