One disadvantage is that most camers have their sensor on the front. I know the 350D has an angle of about 170 degrees where it can be used from. Not that this is a great disadvnatage. But the great disadvantage is loosing the thing. In long exposures I click my wireless remote and then just let it dangle.
Do wireless remotes also work in Bulb mode? <-- this should be looked into as the ability to lock down the shutter it's an important feature of a remote.