For when you next see a headline 'sales' figure and have people with agendas intentionally comparing apples to oranges. 
Sony
http://www.sec.gov/Archives/edgar/data/313838/000114554905001127/k00949e20vf.htm
(page 37)
http://www.nintendo.co.jp/n10/news/050526e.pdf
(final page)
http://www.sec.gov/Archives/edgar/data/789019/000119312504150689/d10k.htm
(page 40 under revenue recognition)
Sony
http://www.sec.gov/Archives/edgar/data/313838/000114554905001127/k00949e20vf.htm
(page 37)
Nintendo* Production shipments of hardware and software are counted upon shipment of the products from manufacturing bases. Sales of such products are recognized when the products are delivered to customers.
http://www.nintendo.co.jp/n10/news/050526e.pdf
(final page)
MicrosoftCONSOLIDATED SALES UNITS, NUMBER OF NEW TITLES, AND FORECAST
http://www.sec.gov/Archives/edgar/data/789019/000119312504150689/d10k.htm
(page 40 under revenue recognition)
Revenue related to our Xbox game console is recognized upon shipment of the product to retailers. Revenue related to games published by us is recognized when those games have been delivered to retailers net of allowances for returns and price concessions. Revenue related to games published by third parties for use on the Xbox platform is recognized when manufactured for the game publishers.