"How does this google thing work? I understand that the most relevant link will pop up under a specific search, but if everyone suddenly googled "kangaroo" and clicked the fourth link whether or not it was relevant, would that link be bumped to the top or are most things just set there sensibly?"
Though my answer is in no way final, I thought it may be of use to more of you than just the person asking that question. Here it is:
And that's just what you can get from professionals in related industries, reading articles, and playing SEO cowboy. Google remains tight lipped for the greater part beyond what you can easy find - arcane mathematical formula and the like - so you have to pretty much reverse engineer based on results, and can have those results shifted on you overnight. Which is a real bitch when you're doing Black SEO ops. (Funny story there, that I can't tell.)"
So, there we are. One more person outside the black box tossing conjecture into the blogosphere. I hope you are entertained by this pseudo-information.