Not at all, a correctly configured router should stop most attempts to break in "uninvited" (if you knowingly or unknowingly install some dodgy software then that is another matter). I don't think Mac users need to be particularly worried at the moment anyway, as the few known exploits around at the moment are really just proof-of-concept type efforts and aren't really intended as serious attacks. As the above article indicates, the Mac userbase is really too small for most hackers to be bothered with. I really just posted the link to help people stop being complacent i.e. just because I use a Mac shouldn't mean that I assume that I am invulnerable to hackers or that my OS is more secure than any other. Sensible practices, such as not clicking on links in spam etc, should be adhered to whatever your choice of platform.
Cheers
Alan