If Yahoo is your home page, your search engine, and your e-mail service of choice, you can install the Yahoo Toolbar and pretty much get a new version of what you already have. The only advantage is that it's always there, even when you're not visiting a Yahoo Web page. Whether that's worth sacrificing some browser real estate for one more toolbar is a question you'll have to ask yourself.
On the other hand, if you don't live in a Yahoo world, I can answer this question for you: It's not worth it.
The Yahoo Toolbar gives you a button to take you to the Yahoo main page, and a pull-down menu for Mail, My Yahoo, Games, and other pages. There's also a search field.
Most of the Toolbar is taken up by something called My Apps--a row of icons for various Yahoo and non-Yahoo web sites. Click an icon, and the Yahoo Toolbar will take you to the appropriate page. Click the down arrow next to the icon, and you'll get a pop-up window of site-related information. For instance, click the Mail arrow, and up comes a glimpse of your inbox. Yahoo Toolbar defaults to displaying six such apps: Bookmarks, Mail, Weather, Facebook, Finance, eBay, and Travel. You can remove any of these, and add more from a selection of 186 others. Newsfeed apps are often RSS feeds, and these can be very convenient; click the down arrow, then pick a story.
One nice feature: When you install the Toolbar, you'll be asked if you want to install the Yahoo Mail Plug-in. If you pick that option, it becomes your default mail application, not only for Internet Explorer but for any program that uses the default mail setting, such as Windows Explorer, Microsoft Word, and WinZip. This enormous convenience solves one of Web mail's biggest problems. Just one word of advice: If you're mailing a file from Windows Explorer, don't select Send To, then Mail Recipient. Select Send To, then E-mail with Yahoo! You'll get better results.
Another installation option allows you to install the Toolbar into Firefox as well as Internet Explorer.
Note: This link takes you to the vendor's site, where you can download the latest version of the software.