As of 3.1, there appears to be a bug in the admin_dashboard_stats filter, at least when used by plugins as directed via the documentation. Here’s what the output looks like.
Hmm yes, the way this filter needs to work has changed in 3.1… The new version of this has you pass a couple pieces of data, but not actually create the link yourself.
What it’s looking for now is:
$stats['exhibits'] = array(5, __('exhibits'));
where the first 'exhibits' is a record type to be passed to link_to, and the array is the number followed by the visible label.
The pattern is pretty simple as long as the link you want to put in there can work with the link_to function. Does that match what you want to do here, or not?
This change was made to improve the accessibility of those links, so the number and the label would both be part of the same link, but I don’t think it was quite appreciated at the time that this would change what plugins needed to do here.