Before the Google alerts filled up with "It's a Boy!" links, they were full of "Geek Cred" stories about Felicia Day's upcoming appearance on the show.
Many of of, of course, love Felicia for many reasons. Buffy. Dr. Horrible. Dollhouse. Eureka. The Guild. Dragon Age. Some of us also love her because she's a reader of popular fiction and loves to tweet about books. :)
Felicia is reported to be playing a hacker named Charlie in the awesomely named episode "The Girl with the Dungeons and Dragons Tattoo."