I use pro-pilot assist on my commute to/from work every day. It's about 30 miles each way of interstate traffic (although I get the carpool lane in the Leaf, so at least traffic is moving at 50+ mph the whole way). The lane keep works great, although I have solid white lines to my right and a solid yellow line to my left, so it's pretty much the easiest use case imaginable. The cruise control works well at the 2 setting, although as others have mentioned, it's focused on moving objects, so if the car ahead of me is stopped and I'm going 50+ mph, the system doesn't realize it needs to stop until after it should've been applying the brakes.
However, keep in mind that the manual explicitly covers this. I don't have it in front of me, but I distinctly remember reading something to the effect of how the feature is intended to speed match a vehicle moving in front of you (including that vehicle stopping), but it's not intended to stop for you when a stopped car suddenly appears in front of you. If you think about it, the car icon is greyed out when there's no car in front of you, which I take to mean that system is currently "off" until it locks onto a moving vehicle in front of you. I mean, between that, the steering wheel sensor, and all the written warnings, I don't think Nissan could be more clear that the system is to make your driving experience easier by not having to constantly speed match the traffic in front of you or make small lane corrections, but it's not intended to allow you to stop paying attention to sudden changes in traffic conditions (like rolling up on a traffic jam when you're going 70mph).
When there's no cars in front of me, I treat the PPA as a normal cruise control. When there's a car in front of me, I let the PPA speed match for me. Ironically, in some ways this means that the system requires less attention when there's a moving car in front of me versus when there's no traffic at all, since adjusting to the car in front of me will allow the PPA to properly slow down in a timely manner if we run into major traffic.
Even though I am more or less satisfied with how the PPA works right now, there are some quirks I've experienced as well. About 20 miles into my 30-mile commute, there's a 1-mile stretch of interstate that's relatively flat and straight, with well painted lines, where the PPA beeps and shuts off every day as if it can't find the road for lane keeping. During this stretch, my cell phone coverage (I've had both AT&T and T-Mobile) drops off as well. I think there's some weird radio interference on that stretch that also screwing both with the PPA and cell coverage.
I do agree that the PPA does not resume speeds fast enough when cars ahead of you speed up, but you can always override that with the accelerator if it really matters. However, I will say this. While it doesn't resume speeds as fast as I would like, it does resume speeds just barely fast enough to keep people behind you from honking
, so relying on it isn't a big deal, since once you get back up to speed you're going to close the gap back to the distance you've set anyways.