I'm with Dinesh.
If they work together and play nice why not.
I've been using the free Avast and Spybot for the past five years. I have never got a bug.
I went to the Avast Internet Security with the firewall about four months ago on my old XP system.
Swithced it over to this new PC with Windows 7 about a month ago.
I also added my Spybot to the Windows 7.
Then I read about the MSE on this forum.
So I have MSE running.
They all behave themselves and work together quite nicely.
Idle has 1.5GB in use. That includes all the ASUS utilities and all the Windows 7 and IE8 etc.
IE8 gobbles up more ram. 118,000K at the moment per Task Manager.
If you want to save RAM dump the IE8!!!