Next to the Web browser, Microsoft Office is probably the most-used computer software product in the world. Its three main components – Word, Excel and PowerPoint – are the top business applications on computers. And the fourth pillar of Office, Microsoft Outlook, is the leading e-mail, calendar and contacts program.

So, when Microsoft makes significant changes to Office, it’s a big deal. And the latest version of the software suite, called Office 2007, due out Jan. 30, is a radical revision, the most dramatic overhaul in a decade or more.

In Word, Excel and PowerPoint, all of the menus are gone. None of the familiar toolbars has survived, either.

In their place is a wide, tabbed band of icons at the top of the screen called the Ribbon.

In Outlook, the Ribbon hasn’t kicked out the menus and toolbars in the program’s main screens, but if you compose an e-mail, or set up a new contact or appointment, you’ll see it.

As if this weren’t enough, Microsoft has also changed the standard file format for Office files. Older versions of Office, on both Windows and Macintosh computers, won’t be able to read these new file types without special conversion software. The new version can, however, read files created in the older versions, on both Windows and Mac, without any conversion software.

After months of working with the Ribbon and other new features of Office, I believe they are an improvement. They replace years of confusing accretions with a logical layout of commands and functions. They add easy and elegant new options for making documents look good. And they make it much simpler to find many of the 1,500 commands that Office offers, but had buried in the past.

So, Microsoft deserves credit for being bold and creative in designing Office 2007. It has taken a good product and made it better and fresher.

But there is a big downside to this gutsy redesign: It requires a steep learning curve that many people might rather avoid.

It’s as if Toyota decided to switch the position of choices on the automobile shift lever, or Motorola decided to rearrange the buttons on the cell phone key pad. Even if the companies could conclusively show that the changes made life easier, many people would be annoyed at best, and furious at worst.

If you mostly compose plain Word documents, simple presentations and plain spreadsheets, the new design may not be worth the effort to master it, and you might want to stick with an older version of Office. People with the new version will still be able to read your documents and you can get free conversion software so you can read new files.

The other group of users who might be better off skipping Office 2007 are power users who know many commands and have customized their menus and toolbars heavily. The new Office is much less customizable.

There are other nice additions. In Word, Outlook and PowerPoint, there is now contextual spell checking, which points to a wrong word, even if the spelling is in the dictionary. For example, if you type “their” instead of “they’re,” Office catches the mistake. It really works.

In addition, throughout Office, there is a function that translates a word or sentence into other languages. In PowerPoint and Excel, there are new, better-looking graphics for charts and tables.

And all the programs have Live Preview, a feature long offered by WordPerfect, which shows a formatting change before you commit to it. You can see what a new font or style would look like by hovering over the choice with the mouse.

Outlook, the least changed of the programs, finally catches up to other e-mail programs with a fast search capability and the ability to preview attachments without opening them.

But the Ribbon is the biggest change. It’s essentially a super toolbar divided into seven logical tabs, which attempt to group similar commands. Each tab brings up a new version of the Ribbon. Common file-handling functions like Open, Save and Print aren’t on the Ribbon. They are accessed by clicking on a big round icon at the upper left called the Office Button, which is roughly the equivalent of the old File menu. Clicking the Office Button also displays a much larger and longer list of recently opened files than the old File menu did, and you can even permanently “pin” files to this list.

There’s no doubt that some functions are quicker and easier in the new interface. Narrowing the margins in a Word document now takes as few as three clicks, compared with up to 14 clicks and keystrokes in old versions.

If you’d like to get more out of Office, especially in the area of how your documents look, Office 2007 is a big step forward and worth the steep learning curve it imposes. If you’re happy with Office now, or you mostly create plain documents where formatting and design aren’t high priorities, it may not be worth the effort to buy and learn the new version.

Walter Mossberg writes about technology for The Wall Street Journal.