How to get a count of number of nodes created per month in views
I just figured it out:


Create a view for all nodes (filtered by type or status if
necessary). 
I use a table layout, enabled aggreation, added field
"nid" with "Count distinct". 
I then add a sort by "post date" with    "monthly" granularity.
Then I added a "post date" field with custom    format "M-Y". I
select "min" instead of "group results together. That's important, otherwise it will not group the results by month