Been using it as my daily driver on both my Pixel C and 6P since it came out. Aside from a few error messages telling me that the clock has stopped or the HBO app stopped I've had no problems with email, sms, phone or other "vital" apps.
Not good. Had it on my 5x and was lagy as hell. 5x is my testing device, I have 6p as my daily driver on M. I do NOT recommend it on a daily driver. Simply too soon. It's still in beta, lets not forget that.
Its pretty stable for such an early release.
There are of course some bugs, as well as some app incompatibilities, but thats to be expected.
Been using it since day one, few minor issues, and found one major issue using the app battery widget reborn, and then setting its notification to the highest setting. It would cause system UI to crash constantly. After messing around, and then adjusting it down from highest, its been fine again.
No April update for it yet, but hopefully soon.
I went ahead a installed Android N. The good news, Nova Launcher works fine, the bad news Free Adblock Browser doesn't work at all, it just crashes. On the browser front I also tried Brave and it's much worse than not working, it took over my screen and I couldn't do anything. I was able to recover by doing a power cycle and then removing Brave.
On another note it hasn't fixed the Verizon problem with Band 2, at the bad site in Nashua NH I'm getting 2M down on a -63 dBm Band 2 LTE, the tower is only 500 meters away.
Been running it on 6p since day one. Not too many issues, definitely improved after second update came through. Cousin also had it installed on his Nexus 6 and not too many issues. I believe he has an MMS issue with using the camera through MMS. I myself haven't had any huge issues and I haven't considered going back to M.
Day two report. It's been stable but I can't say it's an improvement over Marshmallow. I find the notifications more intrusive than before and less aesthetically pleasing. I'm disappointed in the dual window mode, flipping into two window mode is awkward but since this is just an alpha I trust it will get better. More importantly I suspect that multi window mode will never have much utility on phablets and none on puny phones, it's really a large tablet feature, the windows are just to small to be useful.