Been messing around with Impatiens on WHM ever since I got my Witful Belt, and even though it's only 5% total, I must say it feels like it procs more than that.
I mean I see it proc a lot, and I absolutely love it. I get random instant cast hastes/teleports/buffs/cures, all over the place.
Having it running in the background along aside my other gear is very nice.