Agree 100%. I deal mainly with residential clients and almost every infected box I deal with has a current Norton or McAffee subscription. We remove them, run their removal tools since, like a virus, they leave crud behind, and install MSE and ensure the firewall is properly configured. The speed up can often be significant, especially on older boxes, and it's free. I have no problem with MS offering as an OPTION the installation of MSE. I am NOT an MS fanboi by any stretch, but MSE has been great. But it's an AV program and virus writers work to get ahead of them. I've certainly had a few MSE boxes return infected again with scareware. Only so much you can do.
One part of MSE I really like is the ultra simple process for submitting things it did not detect (right in the Help menu) and how they provide you with ongoing status updates as they analyze your submission.
Only thing about MSE is it uses a decent amount of memory (90-150MB) So any box with 512MB is going to struggle and we often encourage clients with 1GB to upgrade to 1GB anyway, even with XP, given the expanded memory footprint of browsers, AV, office, etc.
The only clients we don't encourage to switch are those that actively use Norton's backup service if they have a stout enough computer to handle running N360, etc. Sure they could use MSE, MS Firewall, and an online backup service like Backblaze, but that's just more stuff to deal with and we'll encourage them to go ahead and stick with N360 until such a time that they decide to backup some other way or hit 2GB and don't want to pay Norton for more space. This is VERY rare.
So hats off to MS. Don't care if you bought the technology. MSE is a great tool and I hope they continue to keep it lightweight and easy to use.