Here's a presentation about the ISO 14443 contactless card and security:
http://www.nmda.or.jp/nmda/ic-card/pdf/Vazquez.pdf
It's not a simple as the card broadcasting your CC# to anyone within earshot. For finance transactions it's an encrypted 2-way transaction with the reader authenicating your card and your card authenticating the reader.
To me, it looks at least as secure as internet credit card transactions, and definietly more secure than handing over your credit card to the sub-minimum wage guy at The Ground Round.