With more marketing happening online, the traditional forms of marketing are getting more attention. I recently received a business card that used the back to invite me to a free online demo. I simply had to visit a web page and register with a name and email.
Not only did the use of the business card help to drive me online, but it allowed me to take advantage of a very "special offer". You know as well as I do that the offer wasn't all that special but it certainly got me to take action - online.
Consider your business cards. Are you using them to push information to prospects that don't want your product or are you using it to drive prospective customer's online. Consider a promotion or teaser that can drive anyone who has your card online.
You'll not only have a reason to distribute your business card more aggressively, but you'll leverage a pretty common marketing expense you may otherwise have forgotten!