Why isn't the visits-per-day counter for our site on Area 51 working?
This is a known bug.
It is fixed for site analytics as of some date no later than the 25th May. This has apparently also fixed the underlying issue on Area 51 but it apparently takes a while to update, so we'll need to give that some more time.
To satisfy people's curiosity, we've been averaging around 750 views per day over the past month or so, which is a huge improvement over the previous month.
Update: the stats on Area 51 are now working properly again!