Just like all statistics, these should be taken with a grain of salt, but I think Github's "pulse" breakdowns between Iojs and Node are pretty sobering.
Iojs: 49 authors have pushed 168 commits to master and 572 commits to all branches. On master, 8,474 files have changed and there have been 1,524,012 additions and 708,276 deletions.
Node: 30 authors have pushed 5 commits to master and 95 commits to all branches. On master, 10 files have changed and there have been 294 additions and 36 deletions.
Iojs: 49 authors have pushed 168 commits to master and 572 commits to all branches. On master, 8,474 files have changed and there have been 1,524,012 additions and 708,276 deletions.
Node: 30 authors have pushed 5 commits to master and 95 commits to all branches. On master, 10 files have changed and there have been 294 additions and 36 deletions.
That's for the last month.