If you donate through the Wau Holland Foundation [0], Wikileaks only get money if they provide a receipt for what they spent, and only for things that are in line with the foundations goals. See also this Interview [1] in Der Spiegel about donations.

[0] http://www.wau-holland-stiftung.de/english.html

[1] http://www.spiegel.de/international/world/0,1518,734318,00.h...