This has been suggested several times and I think it's extremely important. I see it as essential for the forum's funds security and I don't see any disadvantages at all. Current treasurer OgNasty agrees multisig should be used.

I would suggest choosing several very trustworthy users and creating x-in-y addresses, where x is at least 3 (to avoid collusion) and y is at least x+2 (to avoid an accident to lock the funds). 4-in-7 addresses could be a good option. Theymos, is there any reason this hasn't been implemented yet? What are the disadvantages? Funds have been lost and more could be lost in the future.