badbadmonkey - 4:13 am on Jun 15, 2011 (gmt 0)
What this means is that the people considered active (no statement as to how many that is or how they are measured) are really active and visit the site every 2 days on average. Assuming that the definition of "active user" is somewhat rational, it's a pretty impressive stat, albeit not surprising.
What it means is that 50% of active users are in fact active.
Without knowing what they mean by active, it's totally worthless. And regardless, you can probably say precisely the same thing about any site with membership.
Looks like this has got to Zuckerberg: