I just installed Blogmonster by JoomlaXTC, which uses K2.

 

But I can't figure out how to remove the item date. I tried "Hiding" everything that has to do with the date/author in the configurations, but the date just won't dissapear!

Try disabling in categories parameters as well.

I've already done that, removed it from Categories & Items. Tried looking at Firebug, and if I remove "<span class="itemDateCreated">onsdag 30. juni 2010 19:46</span>" it dissapears, but I'm not quite sure in which file I can find itemDateCreated..

components/com_k2/templates/default/item.php

& for category layout it is category_item.php

Just remember if you edit the file, and update to new k2 version the file will be overwritten.