Why is VBSeo no longer working for my site?

After we installed it, it worked an absolute treat
we then noticed things level out, then after installing vb4.2 things have been going down hill
are there some settings I should look to change?
any help would be great as I find many of the settings a little disconcerting if not confusing

here is our analytics ... you can see how well things were going for us
Ignore the peaks, they are just from when we have been mentioned elsewhere

I should add, I pretty much left the vbseo settings as standard to start with ...