Sorry to hijack your thread, but I've had some questions from cofounders about screen scraping. Am I allowed to scrape information from their websites and use

Sorry to hijack your thread, but I've had some questions from cofounders about screen scraping. Am I allowed to scrape information from their websites and use it to populate my system? Isn't that effectively what google does? Is there a limit to what is considered acceptable/not acceptable? E.g., is it OK to scrape for email addresses that they publish on their site, but not for their part numbers? Thanks!