As I doubt that the APIs have considerably improved since this blog post http://www.seomoz.org/blog/the-nasty-problem-with-scraping-results-from-the-engines, google scraping is still a big issue and necessary for our daily seo work.
Scraping savely can only work if you succeed in convincing Google that you're a "natural" user and not a scarping robot. How can you do that?
- Search with alternating IPs, from different locations using proxies from the countries where you'd like to scrape from
- don't send too many requests at once from the same source
Consider that, when requesting a URL, the browser sends various information elements to the server, containing, for example, your Operating System, browser version, referer, etc. - every element can and should be changed to virtually change your identity when executing a new search.
- change browsers, browser versions, operating system information, etc.
- take care when changing browser localization values (en-GB, en-US probably don't return the same results)
- have a good network of proxy servers ready to send the different requests with your different identities to