Testing of OmniGraffle 5.2.3 beta 2 went well over the last two weeks, so we're ready to go for a release candidate. As is usual policy around here, we'll let the RC bake for a couple of weeks and then go final if nothing bad happens.
Disk images and release notes covering the history of version 5.2.3 can be found at the bottom of the OmniGraffle download page.