The Implementation shows a ton of foresight, evidenced by the use of Joomla's inherent User tables instead of creating new ones.
Unfortunately it is not perfect yet- Noticeable a BETA version.
The most frustrating bug is in front end submissions. If a user has authoring rights, but not publishing rights, it bombs out after the article is submitted.
Also, no matter who the author is, in the back-end it is listed as an administrator.
I cannot wait for this to be completed!!
We're getting there, don't worry.
As you can imagine, K2 is not only a big component in terms of code but also in terms of functions and how all these combine together. It's natural that there will be bugs, but all will be fixed when v2.0.0 "final" is released. And we're very close to get there :)