I've applied my Beta version of this SP to a low risk laptop. With this version you must back up your existing set-up. In fact, Microsoft don't even give you the option of not backing up! There's confidence for you.
First impressions are that the new security measures are going to cause some grief at first until we get used to the changes.
Read about it
HERE
Oh, and it
didn't do the most important job I wanted from it. That is, fix the problem described
in this bulletin .