I can't say I know of anything except from a few months of rec.photo.digital 
reading, but apparently there are the following caveats to worry about:

-Grey-market goods, i.e. imported cameras with warranties only good if you're 
willing to come to Japan to claim them.

-Upselling-- you order, they call and try and hock you overpriced addons 
(like extra memory cards you can get cheaper at a comp-centric shop), and if you 
don't bite they may find excuse to cancel your order.