Google wont tell anyone the exact details of what search rankings are based on because if they told anyone then people would start playing the system.
Incoming links are good as long as they are legit. Google is onto that trick. Meta keywords in the head of a page are virtually completely ignored these days as they are too easy to game. Frankly most of what is written about SEO is bollocks as far as I can tell.
I dont think it can be kept a secret, particularly as some of the experts who worked with google probably are now working as consultants for SEO companies - the only thing that they can probably hold back on is the weighting of these individual factors in the algorithm. A bit like the coca-cola recipe.
Link exchanges are pretty much useless if they are obviously contrived.
Link exchanges were always pretty inflential until these link farms became abundant - now low page ranking sites have been rendered pretty much useless. However ones from sites like the BBC make a difference.
SEO is bollocks as far as I can tell.
Not sure how you came to this conclusion?