a whiff of grapeshot

I've been absent for a while because I've been too busy with college and work, but I'm back now, hopefully for good. I've got a few upgrades coming soon and also some cool "side-tank projects" I want to share with Reef Addicts. But what really prompted me to log on tonight was this: I've been going to school in the mornings and working mostly the graveyard shift, because of this I don't really have much time to interact with my tank other than maintenance. This evening was the first time in weeks that I've been able to inspect my tank with a flashlight. Well, I was looking for a particular hermit crab (who is M.I.A.) when I noticed this weird thing:

It was hiding on the bottom side of a rock. I did a quick search and found this photo, "club tipped anemone", that best represents what is in my tank. Does anyone know what it is or any information on these things? And more importantly, are they good or bad?