I have a little thing I'm starting to do with my sites where I put popular search terms for the site at the bottom (underneath the copyright). I'm not sure if it's helped, but some of my pages are now in the top 10 or top 20 of Google.
Of course, I'm still most of of traffic from PPC instead of regular listings, so I'm not doing as well as I'd like. :)
If you know how to manage keyword density and content you don't need to focus as much effort (or cash) into ppc.
We use a cumulative keyword density goal on all of our pages of 10%. The site has 3 primary keywords and a dozen or so secondary keywords. On all pages on our site the cumulative keyword density is at least 10% (meaning 1 out of every 10 words on the site is either a primary or secondary keyword).
Pages with alot of content on them are even higher (15-20% in some cases depending on the site). But I wouldn't push it past that. 20% is what I consider the safety limit. Many SE's tend to penalize pages/sites with higher KWD than that because they think it's just a doorpage.