In the early 1980s Douglas Lenat wrote EURISKO, a program Eliezer called "[maybe] the most sophisticated self-improving AI ever built". The program reportedly had some high-profile successes in various domains, like becoming world champion at a certain wargame or designing good integrated circuits.
Despite requests Lenat never released the source code. You can download an introductory paper: "Why AM and EURISKO appear to work" [PDF]. Honestly, reading it leaves a programmer still mystified about the internal workings of the AI: for example, what does the main loop look like? Researchers supposedly answered such questions in a more detailed publication, "EURISKO: A program that learns new heuristics and domain concepts." Artificial Intelligence (21): pp. 61-98. I couldn't find that paper available for download anywhere, and being in Russia I found it quite tricky to get a paper version. Maybe you Americans will have better luck with your local library? And to the best of my knowledge no one ever succeeded in (or even seriously tried) confirming Lenat's EURISKO results.
Today in 2009 this state of affairs looks laughable. A 30-year-old pivotal breakthrough in a large and important field... that never even got reproduced. What if it was a gigantic case of Clever Hans? How do you know? You're supposed to be a scientist, little one.
So my proposal to the LessWrong community: let's reimplement EURISKO!
We have some competent programmers here, don't we? We have open source tools and languages that weren't around in 1980. We can build an open source implementation available for all to play. In my book this counts as solid progress in the AI field.
Hell, I'd do it on my own if I had the goddamn paper.
Update: RichardKennaway has put Lenat's detailed papers up online, see the comments.
Seeing the recent thread necromancy, it looks like this is a much more important question than I realized at the time, since it bears on AI-related existential risk.
The question, to summarize, was, "How exactly do you keep a good AGI prospect from being developed into unFriendly AGI, other than Security by Obscurity?"
My answer is that SbO (Security by Obscurity, not Antimony(II) Oxide, which doesn't even exist) is not a solution here for the same reason it's criticized everywhere else (which I assume is that it increases the probability of a rogue outsmarting mainstream researchers). Better to let the good guys be as well informed as the bad guys so they can deploy countermeasures (their own AGI) when the bad guys develop theirs.
But then, I haven't researched this 24/7 for the last several years, so this may be too trite a dismissal.