zlib can (and is) be used by alot of different programs on many different OS'es. So this isn't a Linux-flaw as such. I can't remember when (if ever) I have heard of a "real" Linux hole. The hole has always been in a third-party software (BIND for example).
And, like it was said, I haven't heard of anyone exploiting this bug yet. And that's the way it is with Linux: holes get fixed BEFORE they are exploited. In Windows, they get fixed AFTER they are exploited.
Red Hat had patches ready before the security-announcement was made. Debian had fixes available about 3 hour after the announcement, with other distros following close behind. Problem was fixed in a matter of hours, end of story.
Now, if some admin hasn't updated his systems yet, he deserves to be cracked. It would really be his own fault. In my case, plugging this hole was as difficult as typing "apt-get update" and "apt-get dist-upgrade".