Illegal?
Not sure the exact circumstances, but in general factual information isn't owned under US copyright and cannot be protected.
Phone directories and search engines are a common example of things that cannot be copyrighted. The source cannot claim ownership of the information to begin with. At most, they own the design and layout. This is the reason meta search engines can exist.
In becoming a user and extracting records in bulk, he may have violated some terms & conditions, but aside from that I'm not sure what Angieslist has that they can claim ownership of. If what he took was factual pricing information, then they may have a weak case.