So far there appears to be just one large national cooperative data collection effort in the world, and that is by seven Japanese ISPs, representing about 40% of Japanese traffic. Results from it are available on the home page of Kenjiro Cho and (in Japanese only) at project site. The latest published report (as of August 2007) from this effort is the paper "The impact and implications of the growth in residential user-to-user traffic" by Kenjiro Cho, Kensuke Fukuda, Hiroshi Esaki and Akira Kato, presented at SIGCOMM2006, which can be found here. It presents data through May 2006. Fig. 1 on p. 1 there shows that in spite of the high penetration of fiber-to-the home in Japan, growth rates have declined from about 100% per year in mid-2002 to 37% in 2005. The average Internet traffic for all of Japan was (based on extrapolating from the data in that paper to the entire Japanese industry) likely about 600 Gbps in May 2006, which is about 200 PB/month.

Kenjiro Cho has kindly supplied more recent data, not yet published, for the same data collection effort, involving the same 7 ISPs. For the four categories of traffic measured in Table 1 on p. 4 of the paper referenced above, the average monthly traffic, measured in Gbps, for the same 7 ISPs (which have recently been reduced to 6, through a merger of two of them), was

Aggregated ISP Traffic, Japan
Date	RBB Incoming	RBB Outgoing	Non-RBB Incoming	Non-RBB Outgoing
May 2006	173.0	226.2	42.9	38.3
Nov 2006	194.5	264.2	50.7	46.7
May 2007	217.3	306.0	73.8	57.8
Nov 2007	237.2	339.8	85.4	63.2
May 2008	269.0	374.7	107.0	85.0

Thus the growth rate from May 2006 to May 2007 was between 25 and 35%, from November 2006 to November 2007 was around 30%, and from May 2007 to May 2008 was about 23% for residential customers, and about 46% for non-residential ones, for an overall average of about 28%.