Several years ago, I heard Colin Camerer give a talk in which he asserted that language and word choice were what defined a culture. Well, if they don't define a culture, they certainly define a search-based market segment.
Google is currently running a beta test for something called Modified Broad Match keywords, and some of the non-profits that work with our students are eligible. The idea behind Modified Broad Match keywords is to give you more control over how Google matches searchers' terms to the the keywords you bid on. As the diagram above shows, Google's default Broad Match will be quite liberal in matching your terms to synonyms, mispellings, plurals, and what not. The problem is that people who use words very different from the ones you've chosen may not at all be the people you're looking to attract. By that very different word choice, they've identified themselves as not part of your segment.
On the other end of the scale, Google has traditionally provided you the option to bid only on exact terms alone or appearing as a phrase in the search term. While this eliminates the possibility of matching people who use very different terms, it also requires you to specify exactly every term variation.
Modified Broad Match is a middle ground. It matches misspellings, stemmings (i.e., different suffixes and prefixes), and abbreviations but not synonyms.
For the careful search marketer, this seems like it could be the right targeting tool to go after those carefully defined segments. I suspect it will take some skill though, and I will be interested to see if my students find it useful.