I'm updated and running on my nexus 4! As with kit kat, the installation itself was problematic. I thought I'd caused a bootloop at one point, because after it took forever with a filled "Installing system updates" progress bar I forced resets and even went into the recovery menu a couple times. Eventually it finished that itself and started booting, but took forever on the fancy 4 colours animation. After a reset that eventually finished too, and 158 app updates later I was in.
So far I've experienced a lot of lagging, and trying to add a widget to the Google launcher home screen resulted in Google Search crashing, but that has gotten less and less as time goes on.
Actually using it, my biggest fear, which was about vibrate/silent, was a result of misinformation. I'm perfectly happy with vibrate being a volume and silent being a setting of its own because of the additional time you can set it for. And priority is a fantastic feature that I've been fons of never since I noticed it in a friend's iPhone and I have missed not having just this past week.
I've uninstalled TeslaLED and disabled Power Toggles and Tasker because of the additions to the OS itself, which is lovely. I like that they've made more use of the on screen keys, moving the keyboard switcher from the notifications. Nice touch. I'm a fan of Chrome tabs being mixed in with recents. That works for me. My favourite feature remains the smart unlock, if only for its novelty. And as I proof read this paragraph, I noticed the new cursor arrow. It's better than the big blue one. Perhaps none of these things are new to anyone reading this, but I'm pleased with L. If only I didn't have to press back twice to get out of toggles. A quick double press doesn't do the trick, unfortunately.
Is there any way of removing things from the toggles pulldown? I tried invert colours and now it's decided to take up residence on that screen. It's not in the way as such (although it does introduce a new line of icons) but its presence is unnecessary.
Edit:
M.Bluth - nope, a downloaded half an app before cancelling and it was fine.
Edit 2: my new night time brightness in Lux is -70%, because there's so much white everywhere in Google launcher. Blinding.