Backlink Question

Before anyone sets off a long story book answer I think we all know, or should do, that backlinks are what helps our sites up the rankings. Backlinks from higher authority sites obviously doing more for our sites than links from crappy sites, for want of a better word.

I have been playing around with a site with 4400 monthly global searches and have the keyword rich domain in .org format. The subject of the site has no financial future ie the adsense CPC is minimal and there is nothing you could really sell in relation to the content, the aim of my test is getting traffic and what gets us up the rankings.

Now, .edu backlinks as we know are highly valuable (or at least from what I read) though they are really hard to get a hold of. Now, I am sure people are aware of ways to getting edu backlinks but dont share them as they are so valuable but my question is at what point when you get your backlink does Google increase your ranking?

This site started on page 4, quickly rose to page 2 with a backlinks package blast and I left it to see what would happen. Invariably it dropped to page 7, 11, 14, then 19.

So then I found a way to find blogs with an edu extension and went on a couple and posted 2 comments. Obviously I got the normal comment will be moderated at some point jargon. Now, do Google count it as a backlink when you put your details in, or when they moderate it? Or when it is pinged? Or any other answer my mind cant think of?