The software I've used has been pretty consistent about Shift+Enter meaning "new line without triggering the Enter key action" and Ctrl+Enter meaning "action" (send the message, go to the next field, etc). The behavior of the Enter key varies from program to program, but I have yet to find a program where Shift+Enter triggered an action while Ctrl+Enter did not. Which software are you using where Shift+Enter triggers an action?

(I do agree that it's hard to remember what Enter is going to do, of course. It's just Shift+Enter where my experience differs from yours).