The main new part to iWork '09 is iWork.com, a document sharing service created by Apple.
Integrated with every part of iWork '09, at the moment, it's a kind of "float it and see" service: Apple has it down as in beta and hasn't specified what future features it will have or what it will cost. If people like it and use it, who knows what will happen? And if they don't, it might just disappear.
Essentially, it's an online collaboration system that allows you to share your documents online so that others can view them, leave comments and notes on them, then download them in a variety of formats.
It works like this: after signing in with your Apple ID and password (you can create one if you haven't got one) by using the Share menu or iWork.com toolbar icons in any iWork '09 application, you can upload an open document to your iWork.com online storage space. This is currently 1GB in size, so Apple might start charging for additional space if it sees an opportunity.
There is a variety of options for uploading: what filename to use, what other users are allowed to do and what file formats to save the document in online. Dealing with a Microsoft Office user, someone who only has iWork '08 or someone who has neither but can read PDFs? Then check the appropriate box and they'll be able to download the online version of your document and use it.
You can enter a recipient, a subject and text for an email letting collaborators know the document is online and what its URL is. This last part is important because each document has a list of people allowed to view the document and each gets a unique viewing URL. If you don't want a 'viewer' to be able to see your document any more, you can delete them from the list of viewers and their URL will stop working.
The iWork.com site is simple and works well. There's a page for managing your online storage. The reproduction of iWork '09 documents is very faithful and the interface simple to use. Tooltips explain the few things that might need explaining, and there's an online help system that mimics OS X's system and gives a better overview of the service.
There's also a sidebar, giving you various options and information, including whose document it is, who can view it, when it was published, any notes that have been added to the document by the viewers or the publisher, a download pull-down that lets you pick the format in which to download the document and an area for typing in document notes.
The downloaded versions of documents will include any comments added to the online version. There's also an optional sidebar for navigating through pages of the document and a pull-down that allows you to zoom in and out of the document.
iWork.com should work in any modern browser, and anyone using an iPod touch or iPhone to view the site will get a customised view, although it won't have all the features, like comments or viewer controls.
There's no way to edit or create documents online, only highlight text and add comments like little sticky notes to the document; you can drag and drop these around the document, but the sticky note will have an arrow pointing to the comment point, wherever you leave it.
Not all text can be commented on, however. Publishers will need to download the online document once it's been commented on, since there's no synchronisation between your local version and the online version.
As far as collaboration services go, this is one of the best: it's simple yet powerful and doesn't try to do too much. Its reviewing tools are far easier to use than both Word's and Acrobat's, as well as those of more sophisticated services such as Google Docs or Microsoft Sharepoint.
What remains to be seen is how many people will be interested in using it and what price Apple wants us to pay for it.