Who said Microsoft was afraid of change? The two most disruptive things you can do to a successful software package are change the file format and change the interface.

Office 2007 does both; plus it adds more new applications to the ever-growing list of the Office System, some essential, some with rather less appeal.

Ignore all the posturing about open standards and open source; the new XML file formats in 2007 Office are a good idea because they save space and give you more chance of recovering data from a corrupted file.

They're zip files, out of which you can extract individual items like images. Businesses can index and tag files or extract information from them directly, without opening them in an application. You know immediately from the extension whether a file has macros lurking in it, which could save you getting infected.

From a practical point of view it's good news all round. Because converters are available for older versions of Office, you can try to persuade friends and colleagues to let you send them new format files. But as many businesses will wait months or even years to upgrade to 2007 Office, they won't become common any time soon.

The ribbon interface

The core Office apps don't have menus or toolbars any more; just a context-sensitive ribbon of tools. Expect to see more ribbon interfaces from Microsoft - and from other software developers because Microsoft has announced the way other companies can licence the interface.

That means we'll see a rash of products that don't benefit from the ribbon interface and some that take good advantage of it to simplify and organise function, although none of them will be in direct competition with the Office apps. That makes this more than an experiment.

Whether you call it user interface or user experience, everyone has an opinion and it's hard to get right. For the apps in Office 2007 that have the ribbon, we would say Microsoft has succeeded. Features that have been in various Office applications for years have been put where you can find them and use them.

Even Bill Gates has found features in Excel he had never noticed before - and congratulated the team on what he thought was something new.

Yes, you'll need to learn where everything is again. And no, not everything is obvious at first glance, mainly because features don't appear until you're in a position to use them, so the Outline tools aren't visible until you switch to Outline view.

It's a good test of how many features you actually use in a program to time how long it takes you to get your first context tab.

Power users who complain features are missing need to use the program to do something rather than just rummage through the basic ribbon tabs; you switch from thinking about how you do things to thinking about what you want to do, which can feel like giving up control but makes you more productive in the end.

And while the menus are gone for good and there's no classic view, you can still use old keyboard shortcuts.

The Quick Access Toolbar at the top of application windows is a fair compromise, using space in the title bar that's usually wasted to remind you which application you're using - in case you had somehow forgotten.

We still want the mini-toolbar that fades in whenever you highlight text to be customisable; if it has the mix of tools you need it's incredibly handy but if it's missing just one of the formatting tools you use the most, it's more irritating than useful.

And it's disappointing that dialog boxes and the occasional task bar have barely changed from the 2003 equivalents, even though you'll use them far less and they're far easier to find.

Outlook only has the new interface for individual messages and calendar items, not the overall application. Look at your Inbox or Contacts folder and you'll see the same old clutter of menus and toolbars; open a contact or write an email and you get the ribbon organisation of Word.

Diehard text fans will miss the option not to use Word as their email editor, but it no longer slows things down, and spell checking as you go is as useful in email as it is in any other document.

One place the new interface doesn't work as well is with add-ons; these are more popular for Outlook than the other Office programs and they're usually toolbars and context menus. Outlook 2007 relegates them to an add-in tab on the ribbon, (unless they're specifically written to work with the ribbon) so they can be harder to work with. Add-in management is also moved from the Options menu.