This product makes changes in security settings, automatic updates, folder permissions, etc., etc., etc. If your Vista system is running well now, it will not be after you install this sorry excuse for a software release. Remember, it is version 1.0 - which is really Microsoft's post beta, and ready for testing by the masses. Much like Vista, it will take Version 2.0 (the soon to be released Windows 7) to fix it.
Again, Microsoft has released a piece of junk that should go through another beta test and re-development before subjecting users to it. There should be no worry from companies like Symantec, AVG or others that Security Essentials will take their business. This product is annoying and will irritate thousands of Windows users. Free does not make it worth the hassle - you'll only get what you paid for with this product.
If you want this product, wait for version 2.0. In the mean time, keep what you have now. For more information, read the Security Essentials FAQ and a Review of Security Essentials.
The cry is free