I am often asked whether web scraping is legal and I always respond the same - it depends what you do with the data.
If the data is just for private use then in practice this is fine. However if you intend to republish the scraped data then you need to consider what type of data this is.
The US Supreme Court case Feist Publications vs Rural Telephone Service established that scraping and republishing facts like telephone listings is allowed. A similar case in Australia Telstra vs Phone Directories concluded that data can not be copyrighted if there is no identifiable author. And in the European Union the case ofir.dk vs home.dk decided that regularly crawling and deep linking is permissible.
So if the scraped data constitutes facts (telephone listings, business locations, etc) then it can be republished. But if the data is original (articles, discussions, etc) then you need to be more careful.
Fortunately most clients who contact me are interested in the former type of data.
Web scraping is the wild west so laws and precedents are still being developed. And I am not a lawyer.