$100 billion from Japan for 400 tonnes of gold works out to about $7,500 per ounce.
http://www.imf.org/external/np/sec/pr/2009/pr0932.htm

What else would Japan have gotten in return for the funds?

IMF was selling 400 tonnes. (32,151 ounces per tonne multiplied by 400 multiplied by 7,500 = $96.45 billion).

Japan was lending money.

What else did the IMF have in the way of assets to sell?
http://in.reuters.com/article/domesticNews/idINLB54061420090211

Japan at 765 tonnes per the latest World Gold Council statistical report would have moved past Switzerland into 6th place if I am correct on Japan buying the 400 tonnes of gold from the IMF.

What you cannot stop, you must endorse.

$7,000 also happens to be the price of a well made suit according to this New York Times article this weekend.
http://www.nytimes.com/2009/02/14/business/14saks.html?em

Conclusions

Buy all the bullion you can carry. Who do you trust? Do you know who your counterparty is? 1 2 or 3 zeroes. $195 trillion in worldwide equities, bonds and bank assets, excluding real estate AND DERIVATIVES according to the IMF. $5 trillion in physical gold. 1344 IPOs so far since January 1st, 2000 in the United States compared to 1600 firms listed on the TSE and 36 gold stocks in the international indexes. 8.4 million CUSIPS according to www.cusip.com and 36 gold stocks in the international indexes. 381 ETF's on the Amex. 36 gold companies in the international indexes.