I just started a single player world on my un-modded client. I have a Macbook Air 2012 running OS X 10.8.2. I had cheats enabled on my world. I spawned in the Plains Biome near a village. I switched to creative mode for a few seconds because I fell down a well and needed to fly out. Then I switched back to Survival. I had gotten some items from chests in the village, and I also had gotten some wood from trees. I started building my house, and I ran out of wood. I went to get more wood from the trees, and found that nothing, not even my hand would break. It would chop once, but would do no more, even if I was holding down on my trackpad. I have never had this problem before. I am running Minecraft 1.5.1.
Unable to break blocks