As heinous as your experience with Mt. Gox has been, that had nothing to do with Bitcoin directly and it is still a viable means. Transfers within the Bitcoin system itself are much more reliable, and just-in-time transfers and withdrawals can be made using preferred exchanges. If a reputable prior relationship is established, there should be no reason for Mt. Gox or any other exchange to withhold funds - especially post-hack. Just-in-time transfers and withdrawals means that a minimum of funds will be at risk at any point.
User -> Exchange -> X
Direct donation via Bitcoin:
Donor -> Bitcoin -> Wikileaks
Withdrawal of funds immediately following transfer:
Wikileaks -> Bitcoin -> Exchange (Mt. Gox, TradeHill, etc) -> local currency
If Wikileaks' use of Bitcoin winds up lending the crypto-currency credibility, there may be some businesses that agree to accept payment in BTC. That would be essentially a private contract between two parties and the validity stands so long as BTCs still have value. This would make the direct donation situation above realistically possible.
Smart management is all that's required.