Some will argue that primaries are inherently more democratic because they allow more voters to participate. Typically, it will take several hours to participate in a caucus whereas voting in a primary can take as little as five minutes. However, a proponent of the caucus system might well argue that primaries can sometimes take even more time , and that just as with a caucus, a great many voters will choose not to participate in a primary and that is their choice.
Proponents of a caucus will often argue that it puts the decision in the hands of people who care and who are better informed. While this is an elitest argument, it is probably also true. People who take the trouble to attend a caucus are probably better informed on the issues than those who vote in primaries, but neither class of voters has a monoply on ignorance.
Another argument that can be made in favor of the caucus system, though I have not heard anyone make it, is that they are more difficult to game. The 2000 and 2004 elections have given most of us good reason to doubt the validity of our elections and there is no reason to think that our primaries are any better. The integrity of the recent New Hampshire was brought into question by a number of bloggers, see for example BradBlog.
In the New Hampshire primary, there were suggestions that the tally had been doctored to favor Hillary Clinton. Though one might at first think that this would imply that the Clinton camp were involved, a second round of thinking was that Republican forces might favor Clinton because they see her as easier to beat in the general election. There is even the possibility that the media might have an interest in having her win because it would extend the primary season and help fill their advertising pockets. This is all conjecture of course, to my knowledge there is no evidence that the count was falsified and certainly no evidence of who might have done it, however there is likewise no proof that the official count was accurate.
Most people who follow these things are aware that Obama is winning and that he is winning particularly strongly in caucus states. In fact he has won twelve of the forteen caucus states if you include his recent win in Wyoming. Obama has won 86% of the caucus states but only 55% (16 out of 29) of the primary states. One does have to wonder why there is such a marked difference between the caucus and the primary states.