The Federal Judicial Center has released its report on post-Twombly motions to dismiss. It is available here.
The study does not include all district courts. Instead, the authors of the study chose the districts with the highest degree of filings. The results show that the filings of motions to dismiss went up. The percentage of the motions to dismiss that were granted, also went up. Similarly, the percentage of courts allowed the losing party to amend their complaint increased.