I started to look at Piwik several day ago and the first thing I am really missing is percentage values - absolute values alone are not enough. The real use of statistics lies in comparison. The only value I see is bounce rate. You could look at phpMyVisites reports for the start.
Also another thing is missing - total values. Take for example ‘Actions > Pages’ report. How many total of pages? How many percentage of this total was concrete page or page group?
And those two things are missing all over.
Also no possibility for deep / broad analysis. Take ‘Visitor browsers’ - widget show only 5 on one page. What if I have to see all of them or at least 100 in one page? The only option is to export data, but IMHO this should be inside Piwik, say clicking the title bar of widget brings ‘normal’ page where user could see all the data or set entries per page.
Also widgets could be configure of how any entries they show.
Also would be nice to have clicktrough ability or at least the (first) referer of the visit (the data is already recorded in database):
Keywords: what concrete pages user landed with that keyword.
Outbound: what concrete page user was on when he clicked away.
and so on.