This is a great new tool. Before this upgrade, the LinkedIn updates feed was a lot like your Twitter feed for two reasons. Many of my connections are also on Twitter and are posting identical updates to both applications. The second reason is the updates were showing up chronologically so anytime you logged in to LinkedIn, you would see only the most recent status updates.
Now, you can filter by many different categories. Just want to see updates that have been shared? You can click on Shares and see better content (in theory) because it was good enough for someone else to share it.
LinkedIn's advance search for profiles is one of the best reasons to use the application for prospecting. Now, you can search status updates with the same amount of filter capacity. Some examples:
Relationship - see updates from people you are not connected to. This was the first feature I found useful because I saw a great blog post from someone who is a 3rd connection. I am following this person on Twitter, but hadn't seen this post on Twitter yet.
Company - see updates from a company you are tying to get as a client or as an employer
Time - filter to only see recent updates
Location - filter to see updates from people in a certain geographic area
School - filter to see people from particular schools
Topics - shows you relevant twitter hashtags. This is a great feature for those of you who are still learning twitter because you can see the hashtags people are using in the industry or keywords you are searching for!
As with other search features on LinkedIn, you can save a search once you have chosen the filters you want to use so you don't have to re-create it each time.
Click on the "NEW" next to the search updates box to view their quick video overview. This is a powerful new feature so you will want to start using it.
1/27/11 edit: I didn't realize this feature was not available to everyone yet. Here's the link to LinkedIn's blog explaining. http://blog.linkedin.com/2010/09/29/linkedin-signal/