There was some discussion today that started around here: http://www.reddit.com/r/Bitcoin/comments/1yj5b5/unverified_pastebin_gmaxwell_irc_log_mtgox_was/cfkze3p and here's some more explanation: https://iwilcox.me.uk/v/nofrac

TL;DR exchanges can prove that:

• they own specific amount of bitcoins
• and that your bitcoins on their exchange are included in this amount

But they are not doing this yet. I'd like to do something towards changing this.

I'll give a shout out on Bitcoinity to the first exchange that implements it, and it will be displayed for a week under the page title (where sponsors are displayed). Another 3 weeks are going to the first exchange that implements it with volume over 1k BTC over the last 30 days. Exchange must include BTC/USD pair and it's not relevant whether it's currently listed on Bitcoinity or not (although it must provide full API - list of latest trades and orderbook).

I'm considering sorting exchanges not only by volume, but first including those that provide such proof if the idea works out.

edit: to clarify, it does not have to use this specific implementation, as long as the one that it uses works as a proof