Q:

What's a good temporal distance to no longer display relative dates?

Relative dates are great to display the temporal incidence of recent activity, but at what distance is it an inconvenience for the user to see a relative date rather than an absolute one?
Let's assume the context is a forum.

A:

This is completely relevant to whatever the dates are associated with.  If it's an update feed (like your SO recent activity), then it may be a good idea to display relative dates by the hour.  If it's articles talking about software updates, then days would be more appropriate...

