I cannot change it - it is around 100 MB at my system. And it is steady after startup - simply the lowest value of used memory the system shows after a while without activity. And of course nothing started by me. The used memory is shown on the desktop on my system all the time. So I do not have to start anything like the Task Manager the see the value what would change it of course.
And there are no left overs.
But it is not so important. Everyone can test for himself to find out the memory usage on his system. I did this 3 times with a clean partition restore (no CIS installation there at all) because I created the install trace and the uninstall trace. And of course I checked the used memory before and after installation. But whatever we talk it will not change that the used memory is now higher by about 100 MB at my system - sorry. If it uses less at your system then be happy ;D