I notice my piwik-checking is very irregular, sometimes I'll check often, then long periods go by without checking. How about a widget that shows some quick "This happened since you were last logged into piwik"-stats? E.g. "Over the last 9 days you had 900 visits, on average 100 per day (up 5 from the last such period), from 14 countries".
(first posted at http://forum.piwik.org/read.php?3,121153,121215#msg-121215 )
Thanks for the suggestion!