While it's not harmless, weed generally isn't all that dangerous in the short term (with the odd exception, usually related to psychological issues; interactions with other medications might also be a concern, but I'm not familiar enough with the research to be certain about that). It's the potential long-term effects of frequent use that people tend forget when considering health risks. Granted, with all of the propaganda surrounding the drug it's difficult to separate fact from scare tactics, but when you get down to it, if you're smoking a psychoactive substance (even a relatively mild one, compared with harder drugs) multiple times a day, there are bound to be negative consequences.
Long story short, practice moderation and you'll probably be okay.