The crowd in a hotel ballroom in Washington, D.C., was rocking on Monday, the 2,000 people shrieking with excitement over federal health-care databases. That could only happen at Health Datapalooza, the annual summit for data geeks, doctors, researchers and patients who want to use data to transform health care — or at least make a buck. Both of those goals are proving to demand a lot more than just coming up with a nifty API and getting the venture capitalists to buy in. Speakers at the Datapalooza gave plenty of examples of how people are trying to use data to make medical care safer, swifter and less expensive. But almost all of these projects are still works in progress.