Comment here expressed concern on whether site is attractive for new users. I would like some statistics to learn more about that.
Per user ids it looks like site has got 5,000 new users this month, I would like to find more about their activity, how many of them are registered, how many asked, answered, commented, suggested an edit, voted etc.
For the purpose of comparison, I would like to also have similar stats on how it was half year ago, one, two and three years ago.
This is how I would want to measure trends in user "stickiness": by comparing how many of users registered in 2010, 2011, 2012, 2013, 2014 visited site for 5, 10, 30, 100 days. SEDE query for this would be a piece of cake if visited days were in schema... but these aren't.