Slightly OT: Does anyone know how RankScanner works? My guess was this but it still seems to work. Their site seems to suggest they have loads of servers, but seems unlikely, I'd have thought Google would have captached them to hell by now. Very good product. I'm curious how it works though.
I also built a rank tracker (WhooshTraffic at the time - no longer around) and we scraped the Search Result Pages as the user would see them, spoofed the session cookie and used human captcha solvers. We would then cache the cookies generated from the captcha solve. It was highly effective and very scalable because you can stimulate the captcha pages easily and out-of-band generate a very large cookie pool by captcha…
Were you scraping with real browsers or something like Mechanize/Curl? Rate limiting at all? Proxies or real servers?