Since the Panda Update things have changed dramatically. Not that it was unexpected. The kind of trash content the advertisement sites had offered no purpose being up on the SERPs.
In all my years I have learned that there are basic principles that the sites should adhere to. This in spite of search engine toleration.
Similarly in case of keyword usage it should be natural. But a large number of similar word will prove disastrous. Use few instances of search terms you are targeting that to keep the topic of the content in mind.