It's white fungus for the most part- harmless, just annoying. Can take the items out and rinse them off to remove it. It is common in tanks with driftwood/live plants that are still relatively new. I did a whole spiel about it to someone not too long ago, but don't have time to pull up all I have on it.
Like I said, go ahead and wipe/rinse it off, but don't be surprised if it comes back- they tend to do that for a while.
Did you add in any wood recently? Is there a way you can get a picture of it? There are actually two different versions, curious as to which one you have..
Last edited by Myates; 03-04-2012 at 03:34 PM.