This is a wonderful extension...the built in commenting and user management and attachments and extra fields are just what I've been looking for. At the last minute on completing a project, I switched back to Joomla core. There is a pecular url problem that I could not find a satisfactory answer for on any forum. I am using basic Joomla SEF, and depending on where I clicked an item link in my site, it made different urls for the item. Example: Clicking an item link from my home page went to "mysite.com/home/item" . Clicking on item from my Article category went to "mysite.com/article/item". (these are abbreviated for example only). If I am missing something, please let me know. Consistent URLs are important to me, but maybe I am wrong. Thanks. It's a great extension and was not hard to figure out.
K2 uses Joomla's built in mechanism to produce the SEF URLs. What you're noticing however is links being created from content which is not assigned to some menu item. If your site has a solid menu structure reflecting most of your K2 categories, then all your links will follow a specific naming pattern. It's all a matter of setting up your content. Additionally, you can use a component like sh404SEF to produce even better URLs regardless of menu structure.