iPhone/iPod headphone controls function w/Focus
I'm not sure if this is old news or not, but I'm using a pair of Sony headphones with controls for iOS devices, and they have partial functionality with the Samsung Focus.
Only the center button works
Same as iPhone controls: single click for play/pause, double click to skip ahead, triple click to go back a song.
Volume buttons do not work.
Edit: The microphone doesn't work either, yet it cuts off the handset microphone. So if you place a call, there's no sound at all unless you unplug the headphones. You can hang up the call by pressing the button on the headphones though.
So... they're pretty much only good for controlling music.
It sucks that they only have partial functionality, I wish I knew of a way to make them work.