The opening scene with Rainbow Dash and Derpy Hooves was storyboarded by Sabrina Alberghetti (the senior storyboard artist) and Nicole Wang, and Derpy herself was voiced (for the first time) by Tabitha St. Germain.
This is the first episode where the fan-favorite character Derpy Hooves gets her first scripted speaking role, AND is also named on-screen by a main character (Rainbow Dash). Derpy started out as a no-name background pony in the first episode of the series, and her "derped" eyes were the result of an animation error (or a purposeful background joke).
Friendship Report: Applejack learned not to run away from her problems and there's no shame at not placing first.
In later airings of the episode, as well as the Season 2 DVD set, the scene with Rainbow Dash and Derpy is slightly altered to have her name removed, Derpy's voice is slightly different, and her eyes are not crossed in some scenes. These changes were made at the request of her portrayal being offensive toward people with disabilities.