The polls are saying that Americans want "change," and Hillary Clinton is responding to those polls with two messages: that she will work for change, and that she has the advantage of experience and will "know what to do" on the first day in office. Ignoring for the moment the issues of whether Clinton really has any experience comparable to being President, whether her experiences in the past are likely to be applicable to future circumstances, and whether she has actually learned anything from her experiences, there are at least two things wrong with those two messages of her campaign.
The first problem is that the two messages are contradictory. A call for "change" is not a call for a particular solution, because if the voters knew exactly what solution they wanted they would vote for the candidate advocating that solution. A call for "change" is instead a call for a new and different perspective, a creative search for a "third way" that is not apparent at the moment. To a voter looking for that kind of new direction, the claim that Clinton already knows what to do the first day in office is not appealing.
The other problem is that the messages of the Clinton campaign are all about the ends and not about the means, about substance and not style, and the desire for change seems to be a desire not just for different results but for a different way of getting those results. Specifically, many voters seem to be tired of partisan animosity and the bickering and acrimony that goes along with it. They don't want to beat Republicans so much as they want to convince them to help advance the common goals shared by most Americans. Barack Obama's message of unity is therefore going to be more appealing to voters looking for change than Clinton's message that her experience in fighting Republicans will make her more effective in fighting them in the future. In touting her credentials of divisiveness, and conducting a campaign of divisiveness, Clinton has completely overlooked what might be the most important kind of change, which is a change in the way we think about politics.
Voting is usually more intuitive than intellectual, and I think that the majority of Democratic voters feel uneasy about the messages about Clinton campaign even if they don't (or can't) explain exactly why they are uneasy. Which is why I expect Obama to win a majority of the delegates elected to the Democratic convention.
Whether that majority will be enough to win the nomination is, unfortunately, a different story.