I have just finished my first 59 minute project with PP CS5, including delivery on Blu-ray. I encountered only one unexplained crash which caused me no problem - I save often.
My first evaluation of the product is that the ability to create Blu-ray disks makes it compelling for me. In addition, I shoot AVCHD at 1920 X 1080, and it does not require me to transcode. This saves me massive amounts of disk storage.
So far as buttons and menus in Encore, you can create them in Photoshop with hot dynamic links. They can be animated or use video imagery. Some here say Encore is complex to use, but it's close integration with Photoshop made it a joy for me.
I am a bit shocked by the lack of documentation. PP CS5 came without a manual, but Adobe has some tutorials online, including a set for converting from FCP, that worked to a degree. I was able to get my job done, but feel I could have finished my project in less time, with less pain if I had the written word.