Constructive Criticism: The play had a test run in San Francisco a few months before the Broadway debut. The producer said that while he felt the New York critics had made up their mind about the play already, the San Francisco critics instead gave advice that helped the play grow to its current form (such as giving Elphaba a stronger role).
"Making Good" was replaced in the final cut by "The Wizard and I" - a recording of it is included on the 5 year anniversary album. The original song in place of "Dancing Through Life" was called "Which Way's The Party" (lyrics also at the same link); that one has not been released in any official form (however, both the sheet music and a soundboard recording of the tryout performance have since been leaked).
The song "Wicked Witch of the East" is in the musical, but not in any of the sound tracks. This is because the lyrics are interspersed with a lot of dialog, and because it contains spoilers that were not yet common knowledge when the cast recording was released in 2003. Still, you can find videos of the song on YouTube.
"No Good Deed" originally had a Dark Reprise of the Unlimited verse that also appears in "The Wizard and I", "Defying Gravity", and "For Good", (it went "unlimited... the damage is unlimited") that got snipped from it because it was decided having the verse show up four times was overkill.
Fandom Life Cycle: Stage 5 for the musical. It's one of the most popular Broadway musicals worldwide and has a steady flow of fan-works.
The play was originally scripted to end with a scene with Elphaba having taken with refuge with the animals and trying to help Doctor Dillamond, but being unable to. Though Schwartz liked the scene, it was chopped because it was felt the play was suffering from too many endings.
There were originally many more direct references in the script to the The Wizard of Oz movie. However, the play was financially supported by Universal Stage Productions, not MGM, so the lawyers put the kibosh on pretty much everything very blatant. About the only one of these that survived was the "lemons and melons and pears" bit.
Stephanie J Bock played Elphaba in the workshop production of the musical before Idina Menzel joined the cast. Stephanie returned to the role for the 1st National Tour.
Disney animator Heidi Gilbert storyboarded an animated version of Defying Gravity.