Many European Nikon websites were down during the past few weeks (especially on weekends). Those outages could be caused by technical issues, but I am not sure how this is possible with the current web servers technology (redundant/backup servers, staging servers for pushing new updates, etc).
Anyhow, the main Nikon Imaging website is also scheduled for a 4 hours maintenance this Thursday:
“Product line up pages will not be accessible due to maintenance during 1PM to 5PM Japan time in Jun. 17, 2010.”
On several occasions in the past Nikon has brought down their websites in order to update them for an upcoming announcement.