Why am I freaked? Because she's a well-known actress that will pull me out of the movie? Sorry, that's not it: It's because she's one of those actresses that appeared on the scene almost 20 years ago and who I (and most other guys) always considered to be very hot. And now, at only 36, she's going to play Spock's mother?
Spock's mother was played by actress Jane Wyatt in the original series as well as in the Star Trek movies featuring the original cast. Since Abrams' intent is to bring new fans to the franchise, if you don't know anything about the character here you go: She is a human from Earth who married Sarek, a Vulcan ambassador to Earth. She gave birth to Spock, who is half-human and half-Vulcan. His human half caused him to struggle with his emotions more than the typical Vulcan as he was growing up.
Spock's entry into Starfleet Academy caused a rift between him and his father that lasted many years, only resolved in an episode of the original series where Spock saved his father's life. On a side note, in the not so great Star Trek V they introduced a character that was Spock's brother, who discarded the Vulcan philosophy of control over emotions.
Steve, one of our regular readers nailed it earlier this morning before the news came out about Wynona by saying that he thought that Abrams would be adding some big name actors to do cameos in the film. :-)