And yes, just got my OmniGraffle 5.0 license. So if you haven't got your yet and you purchased OmniGraffle 4.x after October 31, contact the sales department at OmniGroup :-)
But now to the actual product: I've been working with it since the first beta and mostly really like it. It's a good iterative release with one big feature for me: Support for the binary VISIO file format. Too bad it's online import but I guess you can't have everything ;-) What I don't really like is the way the inspector got changed again. For me personally the inspector of OmniGraffle 3 was still the best since you could easily switch from each panel to another using just your keyboard. Now you just have access to a group of panels. Naturally you can solve this by just using the OSX keyboard shortcuts, but default settings back then just felt more natural to me :-)
Purely from the UI I think that OG5 is a update worth its price since it really cleans up the whole interface not to mention the subgraph feature in OG5 Pro, which I can definitely see myself using a lot in the future.