There's an interesting thread brewing at SEW on the competitiveness of search terms. Member randfish has posted some information on a tool he's developing to provide competition metrics, and of course I can't resist a good conversation on keyword metrics!
References: SEW thread - Competitiveness of a Search Term Randfish's keyword difficulty tool. My take on keyword and search term competition metrics. This is the kind of conversation that extends the art a little bit more. As randfish's tool is further developed, it can only get better. I'm not a big fan of screen-scraping (which IMO is theft), but this tool certainly would lend itself to using Google's API. Not sure why you need to look at multiple search engines to get a coarse measurement of the competition anyway - why not use the one with the largest index, and (other than backlinks) the greatest transparency?
Some additional links on the subject: Pinned thread at HighRankings - measuring keyword competition. SEO Research Labs keyword reports - not a sales pitch here, but a good visual description of how competition metrics are applied.