It took me 220 Dusk Balls to catch Giratina my first time.
That's right,220.
Legendaries in general are a pain in the ass.
In HG/SS? I caught my Giratina in Pearl, so its in the defense form.... that is if you're talking about the game I caught mine in. I actually found him fairly easy to catch in Pearl. like 10-15 dusk/ultra balls.
Palkia was an f-ing cheap shot. They make you fight him right after the Galactic fights! wth, that wasn't fair, and I call shenanigans. I used my masterball then, and I felt f-ing justified. I still regret using my Masterball on Ho-oh though...
The legendary birds were meh. Mewtwo was easier than Lugia. I'm working up the patience to catch the dogs and the red Latias/Latios thingie...
I'd just recommend to the legendary catcher: Patience. Vigilance. and Stock. patience for the long slogs, of getting to the pokemon, and the battle. vigilance, making sure to not kill or be killed, or do anything to lose your oppurtunity to cath it. always save before the battle. Finally stock up on pokeballs of the most advanced power. Dusk balls are a must for caves and night. Ultra balls the standby.