I think the move by Yahoo to take on the Food industry is a great idea. If you look at the cult following that the Food Network has on cable, then Yahoo is definitely entering a market with very little competition. Perhaps even a partnership with the Food Network and Yahoo Food... could make it interesting. I think this may be a way for Yahoo to gain some significant market share in a niche area that Google and MSN probably have no interest in.
This is really where yahoo is pretty strong: being a content-site. This is an area that google has only recently entered with google-finance (very different niche, obviously). The kinds of users that yahoo-food would get is also the kind that are probably relatively stable: they aren't likely to just jump ship when something else comes along - if their community is with yahoo. So I do think this is a good idea.