After reading through the comments here, I went back and took a look at some of the pages on my primary site, checking for the first time the keyword densities of some of my more common entry pages, and saw that I had keyword densities of 45-60%. These pages appear in the first page of the Google SERPS, and consist of about five paragraphs of text, with the keyword in question distributed throughout (probably 4-7% in those parts of the page) combined with a giant table that repeats the keyword 500 times, along with other data on each line (please keep flames about how unwise that decision was to a minimum, my users like the tables). Every keyword density tool I have used has shown differing densities: some include the table, some ignore it, some look at the meta tags, others don't, etc. All I know is that I am not arguing with top 5 placement for these pages. I haven't a clue what the limit is, or what would trip the spam filters, all I can report are my own personal experiences.

__________________
The best way to learn anything, is to question everything.