I "upgraded" to Play 4, and a project I had been working on with East/West Stormdrum 2 went nutty. It froze up immediately upon opening. I uninstalled Play 4 and went back to Play 3, but that particular project still gave me occassional freezes until I committed the MIDI to audio and deleted Play from the session.
To find out if I would have continued problems with my reinstalled Play 3, I started a new project, inserted both Stormdrum 2 and Hollywood Strings, and recorded some parts into MIDI. No trouble at all.
They warn on the Play Software Update download page, "If you are in the middle of a project, it may be prudent to wait until the project is complete."
I have writing projects in various stages of completion utilizing Play 3. I can't very well move ahead to Play 4 if it's going to mess with all of those projects. Unfortunately, East/West doesn't do it like Sonar, where you can keep old versions of the program on your computer. Once you go with Play 4, Play 3 goes bye-bye.