Just a heads up for anyone testing navigation in Moodle - there is a nasty little bug I found today when you attempt to edit the Navigation block to show user history. Check it out in the tracker for details.
Bad news is that once it happens your Moodle site is rendered unusable to all users until you manually get into the database and turn the setting off again. Good news is that from what I can tell you need to be an Admin to turn the setting on in the first place.
Just a word of warning for people like me who are naturally curious and turn stuff on to see what happens!
NB - even better news is that this was fixed today by HQ so will be sorted for the next release. Still worth being aware that its in the initial Preview 4 release (and probably earlier ones too).