That's a waste.
FIREWORKS FOR BLOWING UP ENEMIES INTO OBLIVION.
FIREWORKS FOR MAKING THAT CREEPER EXPLODE TOO EARLY.
FIREWORKS FOR TURNING THAT SKELETON INTO A CREEPER.
FIREWORKS FOR NOT LETTING THAT ZOMBIE GET CLOSE TO YOU.
FIREWORKS FOR SPIDER-PHOBIA SOLUTIONS.
Fireworks in ancient times were weapons; Hence the ancient chinese bazooka. Why not now?
*a couple is sitting on a mountain watching fireworks*
Person 1: Oh look, that one was awesome.
Person 2: Yeah, hey look at that one, its so close...
Person 1: And its getting closer...
Person 1&2: FUUUUUUUU *boom*
This sounds like a pretty fun idea. I'd enjoy it. Even if it had no practical value, making fireworks (and testing out different materials to see the results/color) would be a fun goal.
In response to redhawk, I don't see any threads about fireworks anywhere. One or two where a commenter mentioned them in passing, but never any threads devoted to it. It's a good suggestion. I like it.
That would be really... AWESOME
Especially if we can time everything with redstone. I heard that we could make music in the game eventually. So if you could time the music with the fireworks... what a show...
Sorry for the bump but this would be awesome. Since the dyes minecraft has everything it need to create fireworks.
U could craft it like this (the blue block represents a dye):
 [>>-i>] 
The dye would determine the color of the fireworks and U could trigger it like TNT, by hitting it or by attaching redstone.
I love this idea, however, I don't like it as a weapon without that 1 health penalty - maybe more depending on it's power, kickback, range and probable heavy damage sounds potentially over powered. On a lighter note, maybe you could craft them with dye for colored explosions!
Why do we need more weapons in minecraft? It's about creating. The combat has plenty, fireworks for decoration would be much more in the spirit of minecraft. However, they'd be extremely temporary, so hopefully they'd either last for more than a few seconds or be very spectacular.
Use the idea for colored flares as ammo and apply redstone power and Boom fire work launches till it hits height limit or a block placed above it. Good idea or? And btw I LOVE THIS IDEA!!!!!!!!!!!!!!!!!!!!
I would only care for the fireworks if there was some kind of launcher to send them up into the air. The use of dyes to change the color of the firework is a must. They can to damage, but not as much as TNT. A lagre firework would be cool. Make it out of eight or nine of the smaller ones and it makes multiple explosions. They can be multi colored or just one.
= Paper, = dye
This is how I would make the firework. It would look like a paper ball as an item.