Ok I finally watched the Bonus Disc and here's my review(SPOILERS AHEAD):
Additional Scenes:
No new stuff with Cedric. There's two scenes of the trio talking about Harry's scar hurting and Barty Crouch's death. One scene with the Weird Sisters.One of Harry outside at the Yule Ball. This scene was a little too much for a HP movie. People kissing inside the carriages and foggy windows?
Those are the ones that came up to my head at the moment.
Preparing for the Yule Ball
I really enjoy this one.We get to see all the actors preparing and talking about how they prepared for the Yule Ball. There's Robert/Cedric stuff *squee* .One of my favorite features of the DVD.
Reflections of the Fourth Film
Again, all the actors talk about their experiences in this film and how things have change since the first film. We get to see the actors interacting with each other, acting silly and stuff. Another favorite of mine.There are some cute stuff of Robert in it, like jumping on Stan and kissing Katie on the cheeck
Dragon Challenge
One of the interactive games. I didn't play it because they annoy me
Harry vs. the Hungarian Horntail
This feature is Daniel/Harry centered .Is all about how he prepared for the First Task.No Robert/Cedric stuff (well none of the champions is in it)
Meet the Champions
I love the person who thought it was a good idea to have a segment featuring the 3 champions. I LOVE this one.Period.We get to meet the 3 actors playing the champion Clemence, Robert*squee* and Stan*squee*. It has a MTV Diary feel to it.We see when they arrived to the set to when they leave. I have to say that this feature made me love Robert even more. He's such a dork! I have made some screencaps of this segment but I will post them later 
Lake Challenge
Another game. I didn't waste my time in it.
In too Deep: The Second Task
Yet again another Daniel/Harry centered feature. It shows a little bit of Robert/Cedric, just a liitle bit. It shows how Daniel prepared for the underwater sequence and the special effects in it.
Maze Challenge
Another game...
To the Graveyard and Back Challenge
Yet another game...
The Maze:The Third Task
This one show how the actors prepared for the Maze.There's Robert/Cedric stuff in it!
He Who Must Not Be Named
The title says it all. This one is about Voldemort. From the early sketches to the final look. I enjoyed this one but no Robert/Cedric stuff.
Final Comment:
I have to say that this Bonus DVD really was a lot better than the others. The only thing I missed was an JK Rowling interview.They better have one for the OotP DVD! Also, they need to take out the interactive games. I mean, most of the HP fans are getting old and they rather watch more interviews and behind-the-scenes features. I think everyone should buy the 2 Disc DVD. I really love it
