Ok, so I've been on Android O Beta for about a week now and overall it has not been a bad experience for me on my Pixel XL. A couple of things that I have noticed however:
The battery life has definitely not been as good. I usually run Nova Prime and at first I thought that may be the culprit. I have been using the Pixel Launcher for the last couple of days and the battery life has continued to not be as good as it was on Nougat. It seems like the doze feature is doing what it's supposed to do, but if I'm actually using the device the battery plummets very quickly. I've kept all my settings the same as before too. Screen brightness, closing apps all the time, etc.
Second, the camera has some serious lag when trying to launch it via the double tap of the power button. In trying to catch that quick shot this has been a bit frustrating.
Thirdly, the casting to my Google Home has really been acting crazy. Cutting off randomly, or if I decide to stop casting it will continue to play, and even skipping tracks via the phone is not what it once was (slow response or not skipping at all).
Finally, the Bluetooth connection on certain devices has been just a tad spotty. I realize that a lot of folks have always had complaints about the Bluetooth on Nougat, but I really didn't have much problem. I'm beginning to see some of those effects on O.
I will say that overall I have enjoyed the experience with O and it has been relatively stable for me. These are just minor hindrances and aren't anything that I can't deal with. I think I'm going to ride it out and see how it continues to perform. I'm getting used to the new settings layout and am even beginning to like the new look of the settings menu, quick toggles, etc. I really like the notification "snooze" option too.