I am quite sure someone has already found this simple solution, but when I poked around, I couldn't find it.
Here is my snippet to print out the error messages resulting from a validation as a flash notice:
if @user.save flash[:'notice'] = "New user saved successfully." elsif !@user.errors.empty? flash[:'notice'] = "Could not save new user: " << @user.errors.full_messages.join("; ") end