At my current hospital, the most closest thing to CDSS would be an alert system for drug allergies and potential drug interactions. When doctors are prescribing medicines using HIS system, if there are known drug allergies for a specific patient, it will pop up. Sometimes, some clinicians would just ignore and to be honest, there are prone to be error such as prescribing a drug that patient is allergic to. I have experienced and I think the cause of ignoring them would be that the alert is not intuitive, too much text and irrelevant information and speaking technically, they are too easy to dismiss without user action (such as entering a PIN, or countdown at least 3 seconds, etc.) to tell whether they are really acknowledge or not.
In my opinion, the factor that influence clinical decision support system would be the knowledge and logic behind them provided that (to tell the truth) many senior clinicians are very conservative and most likely to decide which treatment to give to the patient based on their experiences. They are not likely to believe the computer anyway. But for other system such as alert messages for drug interactions and allergies, dosage calculations based on patient underlying diseases or laboratory values are still very important.