As has already been said, this is clearly unethical, and perhaps can even be interpreted as illegal (depending on the legislation in place in your jurisdiction).
in reply to The Ethics of Webbots
I'd have to ask your boss why not just contact the owners of this site and look into an agreement with them? Maybe this has not occured to him at all.
On the other hand maybe he already has done this but his offer was rejected, or they wanted more money than he wanted to spend. Either way, proceeding to scrape the site after failed negotiations would just give the other side more evidence against your side in court. You might want to point out the potential for legal costs to your boss.
I'd like to be able to assign to an luser