Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I use the FW800 port only to run a WD My Book for Time Machine... probably could do it with USB, but both iMac and the HDD have FW so why not? Otherwise, I don't have anything else that uses FW.
 
I use mine for my iSight, Target Disk Mode, and it makes a convenient iPod Charger (For the older iPods that can still charge through it)
It is also great for time machine hd's.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.