When you see really high on-page keyword densities in OptiLink you’ll probably find the the pages are framed and the noframes tag has a very limited string of text in it. Since it is only the noframes tag that the spider is seeing, the keyword density can be very high. But at Google at least there does not appear to be a threshold where some penalty gets imposed. In fact, beyond the title tag, Google does not appear to care about on-page factors at all. At Google, linking is king.