In the latest snapshot lag has seemed to increase significantly, not only for me but for hundreds of others as well. Nothing seems to produce it as I can tell, but things such as redstone contraptions being activated make it worse. The more complex the contraption, the worse it gets. Simple things as breaking blocks also produce lag, but this does not happen all the time. I was not experiencing this problem with previous versions, and have tested and concluded that it is indeed this version that is producing the abnormal lag.