How many search phrases should a single page target?
The over-enthusiastic use of search terms in your TITLE, DESCRIPTION and KEYWORDS tags is self-defeating and is likely to dilute the rank of your site; it is usually better for a page to appear near the top of one search query than for it to appear lower down on several. For this reason it is generally not recommended to target more than a single search phrase or, at most, two or three closely related phrases in the same page.