Do E-Mailed Resumes Receive Responses?

What kind of response do people normally receive from e-mailed cover letters and resumes? So far I have received few responses--nothing--not even quick e-mails saying they aren't interested. I wonder if firms even look at the attached resumes. I get the impression they just delete all of them without responding.

Is snail mail the only way to go? At least with snail mail I normally get formal rejection letters.

What kinds of experiences have other people had with e-mail? I've talked to a couple headhunters who seem to think it's OK to e-mail. It's certainly useful for me when firms ask for undergrad transcripts and writing samples. It's much less expensive to send a full application by e-mail than mailing 20 pages.