Did I write that?
Must have done. Anyway you can only have PD9 or PD8. They can not both coexist on the same machine as an application. That is the bad news. The good news is, based on my experience, I have not had any issues with some of the 'simple works in progress' that I had on the go. The .pds files that I had finished or was in mid stream on with PD8 worked fine with the new PD9. I always make a copy of stuff I have invested many hours in but this investment was not lost as PD9 just read the PD8 file.
As far as issues go, touch wood, I have not had any but I am running a 32bit OS so the PD9 will be 32bit. In my set up it does seem to be an improvement on the older PD8.