By Fenrir.Terminus 2012-12-01 16:10:13
There are some that are just while equipped, even though they augment the ability and not the length of the ability. But, the only ones I can think of (and I could be wrong, anyway) are all monk abilities - Focus, Dodge, and Counterstance.
I've never tested them myself, though - it's just been the way I've always done it. But, monk was my first job and I was really surprised to learn that a lot of gear had to remain equipped to keep the effect enhancement.
Oh, then there is Ravager's Mufflers +2, which don't have to be worn on activation at all or during weaponskills - but do need to be equipped during tp phase in order to get the extra boost to weaponskill damage.