Blog Post Comment
The biggest difference is portability. Since it's a widget, you can now put the personalized activity stream anywhere you want in the interface. Also, I think it appeals to people who are more used to the "feed" mentality, where you can see a page with "just your stuff" on it. You don't have to turn the personalized activity stream on or off, it should just be there if your users want to see it (if you are using the Activity Stream at all, which you turn on or off in the Structure area of...