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Receptional_Andy - 2:21 pm on Nov 4, 2008 (gmt 0)
700,000 doesn't seem like an insurmountable task - unless you are using phrase or title matching. These are simple searches that are better than just a default search to estimate competition, e.g. intitle:"green widgets" [google.co.uk] Pages mentioning the keywords (in sequence) within the title of their pages can reasonably be seen as competing. Although this doesn't take into account the many factors affecting the performance of those URLs - they could all be very poorly optimised. Of course, next to nothing is too competitive, other than popular brand names and the like - it depends on your site, and how effective you think you are at SEO.
How are you measuring the monthly searches and competing pages? If your measurements are not reliable, then clearly this will not be able to inform your SEO efforts.