Portal:Characters/Did you know
...That actress Grace Park, who currently plays Sharon "Boomer" Valerii, originally auditioned for the role of Dualla, and Kara "Starbuck" Thrace? Park originally tried out for Dualla and didn't get the role, but director Michael Rymer liked her performance, and asked her to return and audition for the role of none other than Starbuck. Park was actually one of two finalists for the role, the other being Katee Sackhoff, who ultimately got to be Starbuck.
However, Rymer and the writing team were still so impressed with her that they asked her to join the cast to play Boomer. Grace Park actually never gave an audition for the role of Boomer, because she had already done ones for Dualla and Starbuck and the production team already knew her acting range, but as a result she didn't actually sit down and read the parts of the Miniseries script containing Boomer until after she was cast in the role, so she was surprised by Boomer's revelation as a Cylon at the end.