“Wow, this webinar looks really helpful and it’s free!”

ImageWell yes, you don’t have to actually shell out any money for it, but these days nothing is really free. Be aware that along with the information will come the sales pitch, follow-up emails and oddly timed phone calls, especially if you’re on the West Coast and the company is on the East.
So sure, sign up and learn stuff, but don’t give them any more information than necessary, you can always follow up with them later. They will make sure you have their contact information.