The IMF has a great page with everything you’ve ever wanted to know about MetaMoney.
The SDR is an international reserve asset, created by the IMF in 1969 to supplement the existing official reserves of member countries. SDRs are allocated to member countries in proportion to their IMF quotas. The SDR also serves as the unit of account of the IMF and some other international organizations. Its value is based on a basket of key international currencies.
The allocation of currencies in the SDR is revised every 5 years based on the relative importance of currencies in the world’s trading and financial systems. The latest review of the SDR was in November, 2005 where the Dollar, Pound, Yen and Euro were maintained as the SDRs basket of currencies.
The SDRs currency mix is reviewed every 5 years, so come November 2010 (just after the Shanghai World Expo), expect to see the SDR expanded to include Canada and Australia, which would even out the value of SDRs when growth in commodity markets outstrip growth in share prices.