The role of Naomi Bennett was played by Merrin Dungey in the pilot episode's "Grey's Anatomy" (2005) {The Other Side of This Life: Part 1 (#3.22)} and "Grey's Anatomy" (2005) {The Other Side of This Life: Part 2 (#3.23)}.
The character Sam Bennett's nickname/pen name Dr. Feelgood is most likely a reference to the album 'Private Practice' by the band Dr. Feelgood (II) released in 1978.
Sarah Drew plays 2 different characters on "Private Practice" (as Judy, a young, pregnant college student), and Grey's Anatomy (as Dr. April Kepner, a series regular in season 6 and 7).
Amanda Foreman plays 2 different characters on "Private Practice" (as Katie Kent, Violet's patient, who attacked her (the end of season 2)), and on Grey's Anatomy (as Nora, wife of a guy with no arms (season 7)).
At one point, Sam Bennett played by Taye Diggs tells Pete played by Tim Daly that he likes Pete's new girlfriend, Lisa. Lisa is played by Diggs' real life wife, Idina Menzel.
For her role on Private Practice as Dr. Amelia Shepard, 'Catarina Scorsone' was introduced to Shonda Rhimes by the director/actor Eric Stoltz, who had worked with her ten years before and remembered that she resembled Patrick Dempsey. She won the role and is now a regular on the series.
Paul Dooley played the dad of Brian Benben's character on HBO's "Dream On".