I agree that, as far as Yahoo is concerned, the TOS rules out web scraping. Nonetheless, I think it is very difficult to decide if scraping constitutes using an interface other than Yahoo's. You could argue that the TOS implied that the user wasn't allowed to delve into Yahoo's system thus bypassing their interface. It is moot really, since I doubt the OP has the resources to fight Yahoo on the semantics should he end up in civil court.