Note: Those correctable errors (reverse and U-turn connections, soft turns) are there on the white road images (streets) but the color highlights don't show. You see them when you click on the junction. So there can be tons of editing to do on neighborhood streets, which are usually accessible to low-level editors.
As someone who early on made common mistakes such as drawing in detailed parking lot roads. let me offer this excuse: It's not entirely obvious to a beginner that this is a problem. The little quick-start video you watch does say you can draw in "the main internal roads" in a parking lot. Yes, the Wiki explains this more clearly, but frankly, it takes a while to work your way through the Wiki.
I think Waze needs to offer better tutorials -- common editing mistakes to avoid, and such. The fact is, at some point it will be impossible to get enough editing opportunity to give you decent hands-on training. Some other means of training new editors will be essential.
Oahu, Kauai and Lanai, Hawaii
iPhone4, iOS 6.1.2