Puzzle & Dragons was released in the Japanese App Store in February this year and on Android in late September.
The title hit 1 million downloads in mid-July, 2 million on October 20, and maker GungHo says the 3 million milestone was achieved on November 5 (260 days after the first version was pushed out on the App Store).
There can be no doubt that the TV commercials GungHo started airing in mid-October contributed to the growth.
Here is the first one again:
Here is the new (second) one that advertises Puzzle & Dragons on Japanese TV since the end of October:
Puzzle & Dragons in English is scheduled to go live this month.
Via Social Game Info