2013-06-28 Update: NZ search and rescue folks haven't given up though a new search today was unsuccessful.
It is with a heavy heart that I pass on this information. There is a report that the boat Evi Nemeth was sailing on has not been heard from since June 3rd. The New Zealand Herald seems to have broken the story first.
Evi co-wrote the groundbreaking book, "UNIX System Administration Handbook". It has been used as a textbook and outside of schools by nearly every Unix/Linux sysadmin I know. It meticulously covers every popular Unix varient of its day. (In the 1990s there was a lot more variation between Unixes). Since its publication there have been many updates and even a Linux-specific version.
Evi was a mainstay at the Usenix LISA conference. Every year she would show up with a number of students who would get free admission to the conference in return for volunteering. Many of these students have gone on to be well-known sysadmins.
In 1993 she received the USENIX/LISA Lifetime Achievement Award.
When Evi retired she sold her house and began sailing around the world. She is 74. You can read more about her on the wikipedia page about her. (It's a good read. I highly recommend it).
I hope she is ok. My thoughts are with all of her family, including her past students. Let's hope New Zealand's coast guard finds her soon.
As an IT person about to embark on a similar voyage, I hope she is okay!