It has special features on the single disc, with the 2disc version having an additional four featurettes and the blu-ray version having two extra items on it.
I got the details from: http://www.cinemablend.com/dvdnews/Juno-Has-Triplet-DVD-Editions-9189.html
Special Features - Juno Single Disc: Commentary By Director Jason Reitman And Writer Diablo Cody Deleted Scenes:Mrs. Rancik /Juno Hitchhikes/Intro To Family/Carry Chair To Bleekers - Sit In Car Drinking/Café Triste Bleeker's Bedroom with Juno/Lorings In Bathroom/Mark Plays Guitar/Juno Plays Guitar/Montage/Mark's Loft Gag Reel Gag Take Cast & Crew Jam Screen Tests
Special Features - Juno Two Disc: All of the above, plus... Way Beyond "Our" Maturity Level: Juno - Leah - Bleeker Featurette Diablo Cody Is Totally Boss Featurette Jason Reitman For Shizz Featurette Honest To Blog! Creating Juno Featurette
Special Features - Blue-ray All of the above, plus... Fox Movie Channel Presents: World Premiere - Juno Fox Movie Channel Presents: Casting Session - Juno