When Microsoft reset development of Windows and other core products in the wake of the Windows XP UPnP fiasco, it ushered in the current era of "Trustworthy Computing" that we're arguably still living within. As part of that reset, it added a number of security features to Internet Explorer, which it delivered as part of Windows XP Service Pack 2 (SP2). Key among these was an Information Bar that sat at the top of the broweasy to ser display area.
In that version of IE, the Information Bar provided access to the browser's then-new pop-up blocker. Over time, the Information Bar became a central bit of blocker UI for such things as downloads and even browser plug-ins. It was so good, in fact, that every major browser maker copied it for their own products. Today, you'll see a near perfect copy of the IE Information Bar in Mozilla Firefox, for example.
In Internet Explorer 9, Microsoft has dramatically changed the behavior of this control, which has been renamed to the Notification Bar in this release. Under the covers, IE 9 treats notifications just like it does most other things, in a minimalist fashion that is designed to prevent distractions while browsing. So there are fewer notifications than before, yes, but perhaps more important, when those notifications do occur, they are less disruptive and won't typically prevent you from browsing the web. (One major exception to this is serious security threats: In such a case, the new Notification Bar will, in fact, halt the proceedings.)
Also in keeping with the overall IE 9 "get out of the user's way" mantra, the IE 9 Notification Bar has been moved to the bottom of the browser window where it's less likely to distract you when it does appear. As such, it is very subtle. Perhaps too subtle, actually: It's very easy to miss, even anwhen you know its coming, such as when you trigger a download. Fortunately,that little issue has been addressed in the final version of the browser, as we'll see.
Gets out of the way ... Unless it doesn't make sense to get out of the way
One of the major considerations for the new design, of course, was that it not stop a page from loading or prevent the user from doing what they were doing; i.e. reading the page in question. With previous versions of the Information Bar, some notifications were modal, preventing the page from continuing to load until the user addressed the notification. This is (mostly) no longer the case. So if you browse to the Apple web site, for example, you'll still get incessant notifications about enabling QuickTime. But you can safely--and easily--ignore them.
The Notification Bar also appears less frequently. In previous versions of IE, for example, an Information Bar would pop-up if you tried to navigate to an intranet site (a web URL without a .com or similar ending). IE 9 instead automatically resolves intranet addresses and doesn't prompt you.
One thing Microsoft changed during the beta,based on feedback (including in this very article) is that the notification bar will now throb in an orange color if you ignore certain notifications for too long. So, for example, when you have triggered a download but not OK'd it, the notification bar will throb after several seconds just to remind you that you started something.
The new Notification Bar is also designed with normal users in mind. So the messages are written in plain English--or the language of your choice--and don't present a bunch of technological gobbledygook.
Occasionally, the IE notifications system will need to pop-up a dialog box instead of using the Notification Bar. The most common reason is when a web site stops responding. In previous versions of IE, the user would be confronted by an "Internet Explorer is not responding" dialog. But in IE 9, this changes to "\\[Name of web site\\] is not responding" and in most cases, IE will recover and redisplay the site correctly. So why display this message in a dialog? The web site crashed, and the IE frame may be unavailable.
Like other IE features, administrators can customize how the Notification Bar works on PCs throughout their environments using Group Policy. For example, you can disable Add-On Performance Advisor notifications (see below) if you'd like.
Common Notification Bar scenarios
Nothing dramatic or unexpected, but here are some of the more common times when IE 9 will display the Notification Bar.
Save a password. When you enter a user name and password at a web site, the Notification Bar will appear and ask you if you'd like the browser to save this information so you don't need to re-enter it later.
Download a file. IE 9 features a new Download Manager, and it integrates with a reputation service and the browser's SmartScreen filter to help prevent you from downloading any dangerous (or at least unknown) files.
Add-On Performance Advisor. Every time you start IE 9, the Add-On Performance Advisor gauges the performance of the various add-ons you've got configured. And as is (perhaps too) often the case, it will trigger a Notification Bar message that one or more add-ons are loading too slowly.
Default browser. If IE 9 is not set to be the default web browser, it can display a Notification Bar message asking if you'd like to change it back.
Overall, the new Internet Explorer 9 Notification Bar is a nice addition to the browser. It is, perhaps, a bit too subtle, even for those moments when you've initiated an action, like downloading a file. This may be a matter of familiarity. But then an important UI like this should be as intuitive as possible. It's very close.