How effective are download cards?

Unless you're already a known quantity (or have labels/publishers demanding sales metrics) it would be cheaper to just print up business cards with a d/l link.
 
I agree as well, the price difference is insane. I'm definitely going that route for promoting freebies.
 
Seems sorta silly to me. I'd just get a business card done like the guys above said. Put a QR code on the back that goes directly to the download link and you're done. Unless you're wanting to use this for CD sales, instead of having physical discs. Then I could see spending a little more on these and giving them to paying customers at shows, but personally, I'd rather just get a disc.