Since my projects also need's a good page ranking this is a no go for me and I have to switch to another tool. (As long as the support from K2 is also very poor as also others writing herein.)
The only thing I want todo with this posting is to get the SEO part in mind of each who is on the way to try K2.
K2's SEO is not just great, it's in fact amazing. For 2 reasons primarily. No.1 for its native URL construction (to the limit the Joomla! API allows it to be) and no.2 for it's HTML construction with the correct use and ordering of HTML elements.
If by SEO you just mean the URLs, then I suggest you try other extensions before moving away from K2 as you're in for a big surprise! What do I mean? If you don't create menu items to some Joomla! component, yet you retrieve this component's content from some module, you're bound to have /component/name/whatever in the URLs.
So do some homework first before judging something badly.
I'll say this now and I'll keep repeating for a very long time to come: it's no wonder why ALL today's big/popular Joomla! sites are built with K2. ;)
One final tip: Wanna improve your URL SEO drastically? Grab a license for sh404SEF or AceSEF. They both work flawlessly with K2 as we work closely with these 2 dev teams.