Some insist that he is still waiting to allow more people to be saved, but it is not clear that this is happening. People like Harold Camping are causing more people to doubt than believe. Events in the world are making people more skeptical. Furthermore, population has been growing faster in recent centuries and decades than ever before. This is actually making the job of saving all those people harder than ever. It would have been much easier to have come shortly after the death of Jesus, or at least after Christianity became the official religion of the Roman empire.
Others just insist that god is really really slow. They say that it takes 1000 years to equal one God day. There are sloths and inch worms that could beat god apparently. Doesn't this make God guilty of the sin of "sloth" for going so slowly about handling things? I must have missed the part in the Bible where it said God's butt was made out of lead. Seriously, he has not shown a good hustle. That is not what we would expect from a perfect being. He needs to get a move on.