It depends on what you do with it. I scrape lots of websites which have TOS against that, but its for my personal use only, and i'm just saving myself few clicks of the mouse. I'm not generating any extra traffic or doing anything maliciouse, so i don't consider it unethical (i'm just browsing).

However, if I were to try and somehow make money with this data, I would consider it unethical (and IANAL, I'd probably be legally liable).