There are certainly a few things to keep in mind. Many physicians, for example, do not like the way that using an EHR system interrupts the normal workflow of a patient visit. In addition, if one hospital department is using an EHR system, but another department is using a different system, or isn't using one at all, then information exchange is just as difficult as it was before any technology was being used. It also takes time to get used to using an EHR system and, thus, to reap the benefits -- for some providers, achieving ROI takes years.
Many of these weaknesses can be avoided, or at least downplayed, by taking a thorough approach to the purchasing process. You should spend a lot of time researching EHR vendors -- there are hundreds, after all -- to ensure that you find an easy-to-use product that won't disrupt existing workflows and business practices and cna share information with other departments as well as business partners. Doing so will make that ROI appear much faster.