Totally depends on the type of page - if its the index page to a large site that contains many different keyword pages then you can get away with a lot more - and even more importantly is what you do after you start getting referrals from the SEs. Take a look at your raw logs after you start getting hits and see what people are finding you for - then do some refining to the pages to either strengthen the keyword phrases or add more that you think would fly.
I can show you examples of pages that can target 300 phrases, then I could also show you pages that are script generated to targe one phrase and do it over 300,000 pages for different phrases - it all depends on your needs
