Warning: photo loss on disabling Google+
I'm not sure how widely this may affect people but given that I'm running the PA 4.0 beta 2 on a Nexus 5, I thought I'd start here.
Essentially it's fairly easy to unrecoverably lose photos (one by one) using the PA GApps photosphere camera if you have Google+ disabled.
I had disabled it from the Settings/Apps screen as I felt I had no real use for it. I'd left all the other Google stuff working.
No obvious side effects until I was taking photos today (of my newborn son!)
On the camera app, when reviewing a photo, the top left icon that looks like a multicoloured windmill (with a backward arrow) is apparently supposed to take you to Google's Photos app. This appears to be part of the Google+ apk. I used it as I thought it would get me back to taking more pictures. Instead, with G+ disabled, it appears to permanently delete the photo you're currently looking at (at least I've not found where the photo goes!)
With G+ re-enabled it works to take you to the photo app as intended.
So looks like the G+ tendrils have found me after all; luckily I only lost a few irreplacable photos (but I'll take more!). But consider this a warning to be very careful if you disable G+ yourself.