input on the idea please?
apsurd: I think this is definitely an area worthy of taking on, but like another comment said, be prepared for it to take years to mature.I've thought about this problem a bit as well mainly from the position of "you don't know what you don't know". This has always bothered me in terms of self-motivated learning. Google has changed the world by enabling people to learn almost anything online. There still exists a problem though in not knowing what search terms to enter into google? If I don't know anything about sql and database normalization how  am I supposed to use google to find what it is I don't know?My thinking led to a service somewhat like yours. A kind of collaboratively curated "basecamp" for certain topics. I would suggest concentrating on one specific area of knowledge like "computer science". So for example there would be vague things like "Overview of the internet" which would branch off into what a web app is, html, css, browsers, protocols, what a database is, what is mysql , and eventually "database normalization" etc. I think its useful to create properly formed structures of information. That way when you navigate the information you can navigate back up the tree if you need more prerequisite knowledge and then  go further down into specifics once you understand your node. I also like the idea of a an overview "glossary". Don't you think that every discipline has its own language? It's own lexicon of slang and sayings. Even here in hacker news: PG, ASK HN, ror, a/b, seo, CS, machine learning, GAE. I have to be honest here and say that when I first came to HN I didn't think much of it at all because the front page looked like a foreign language to me. "I don't get it" I would think. That's because I was unfamiliar with the language and terms. So I think something as simple as a glossary would make things a lot easier for some people. 
Database: mysql, normalization, key value store, index, foreign key, tables, rows, locking, read, write, etc. 
If nothing else it would act as a starting point to start a google search party.Yes a lofty goal indeed but I think it would be very impactful.edit:A lot of people would point to Wikipedia to solve this problem but as I'm sure you've figured out, wiki functions as a database of nuggets of information that possibly link to one another. I'd argue that hierarchal structured information (or what you might call a guided lesson plan) would be a lot better in terms of actually learning the material. Also I imagine a world in which these lesson plans were curated by people who have "been there before". I can't tell you how many times I have studied something in a book, looked it up online, tested it out for myself, spent 2 more weeks thinking about it and perfecting it, AND THEN sometime down the line later, some guy somewhere mentions the same lesson i learned in a 5 minute conversation. He literally tells me everything i know in 5 minutes, because he's been there before. And I could probably do the same for other people regarding my own domain knowledge. Need to know how to print t shirts? I guarantee you  I can give you a crash course in an hour that will save you months of trial and error.