Both the European exchange points providing IPv6-specific traffic reports showed an increase in IPv6 traffic on World IPv6 Day. AMS-IX showed a a small increase (peaking at 2.9Gbs), but may not be statiscally significant. Based on looking at the year-to-date IPv6 traffic, it looks like the jump in IPv6 traffic started in February 2011 with an increase in peak usage from around 1.8Gbs to around 2.6Gbs. That roughly matches up with the time of the IANA IPv4 free pool exhaustion. DE-IX showed a marked increase in traffic appearing to at lease double its previous reports. It seems clear the community that used DE-IX was using the day to learn more about IPv6.
Ars Technical offers this summary.