There is a long, long troubleshooting thread at XDA
here.
And also a thread on Google's codebase for Android
here.
The tl;dr version: there seem to be two distinct issues. One is slow storage, which may vary across devices and is compounded by background sync and filling the storage. 2 programs which have a big impact on this are Currents and Play Magazines. If you're having issues, try disabling both of these and see if it helps, also try to keep at least 3GB of storage free on your device. That seems to be the issue which is fixed by a full reboot. My gut feeling is that it's poor implementation of garbage collection on the storage, which should be fixable with a software patch, but that's just gut, I could be way off base.
The second issue is lack of responsiveness which is fixed by turning the screen on and off. I've seen suggestions that this is a hardware defect, a bad ground in the screen and may be something that needs to be warrantied. That seems more speculative, though.
FWIW, my Nexus has both issues, but to a manageable degree so I haven't replaced it, yet.