There seems to be a lot of people on here who know a thing or two about martial arts and Japanese weaponry. I've taken only Korean martial arts and know very little about Japanese combat so bear with this basic FAQ about a katana.
(I won't get into the history of it, suffice it to say it's frome Japan)
The katana
It's a sword. It's long, thin, curved (more like an arch), and really sharp on one edge. One edge is dull (The concave edge) and the other is razor sharp. It has a long hilt and no finger guard to speak of. It weighs quite a lot more than fencing swords, about 5-6 lb. Traditional katana's are usually beautifully decorated.
My view
It's a giant skinny meat-cleaver.
Use in combat
Offense or defense:
You can tell whether a sword is offensive or defensive from the size of it's finger guard, the larger and more protective, the more defensive. The katana doesn't hardly have a finger guard.
Stabbing:
Stabbing's not it's forte. You have to stab like Saito's Gotetsu from Rurouni Kenshin; turn it on it's side and put all your power behind the hilt. Because of it's arch and length a lot of your power doesn't get fed all the way through sword. You also have to stab pretty deep, which isn't good considering it's weight.
Slashing/cutting:
This's what it's good at. One razor sharp=won gud kut. In 'Tommorrow never Dies' James and the bad guy are fencing, the bad guy grabs a katana and slashes James's blade off. That's how it supposed to be used, one good cut and there down. You have to take a wide stance and constantly switch your weight around to get power behind the slash.
Sweet if you nail 'em.
Pros
It's sharp and areodynamic. Good range. One good slash'll drop most guys. Stabbing not to bad if you can get it in at the right time. It's weight is both a pro and a con really.
Cons
It's heavy. I mean, I'm not small, but this is tough for me to get around quickly. The guides I read say to, 'Pull your katana out in a beautiful arch-like slash and gracefully flick the blood from your blade before returning it to the sheeth'. If you can 'gracefully flick' that thing I'll give you $10. Also, it's bad at close range combat; no finger guard. I like my finger guard.
Questions or comments?