You could argue that dollar cost average is market timing, which people warn about. "You can't time the market". Or can you?
By putting all your money in now, you recognize that the long-term trend is up, and you are ready to withstand a drop in the short term.
If you fail to invest all your money right away, it is because you are concerned the money will go down at least in the short-term.
Dollar cost averaging to me is just a cop-out. You're not willing to invest it all, because you are concerned it will do gown. If that if the case, why are you investing any of it at all? And don't give me the "if the value goes down I am buying more and more shares each time" argument - If the value goes down you lost money and would have been better staying on the sidelines.
Bottom line, as much as we would like to buy at the bottom and sell at the top, we aren't really able to do so. We can try, and we each have to invest according to our personal risk tolerances which differ. But in the end you have to decide something and implement it. And it doesn't have to be all or nothing, just wanted to give some food for thought.
One more thing: people that have regular contributions out of their paychecks to their 401k's aren't dollar cost averaging. They are putting their money into the market as soon as it is given to them.