There are plenty of reasons to buy Microsoft Office. There are just as many reasons to do the opposite.
While the Mac community awaits the arrival of Office 2008 for OS X, there are some viable alternatives to use now and maybe permanently.
Open Office is a full-featured, open-source, free software suite of programs that read and write Microsoft Office compatible documents. The software project was founded by Sun Microsystems and runs on Windows 98-Vista, Linux, Sun Solaris, FreeBSD and OS X under X11 Developer's Tools.
Think Free is similar to Open Office in many ways except for one. Think Free is an online suite of software that creates documents compatible with Microsoft Word, Excel and Power Point. Users currently get 1GB of free online document storage. Another phenomenal benefit of Think Free is the ability to collaborate online using group editing and file sharing. There are many other benefits as well, and they're free to use. Think Free is still considered "Beta" software. You can also purchase a desktop edition for $50.00 that installs on your hard drive. There are other products available by Think Free as well that are worth looking at.
Google Docs is much like Open Office and Think Free. It's owned by Google and you need either a Google account or Gmail account to access it. Users can share and collaborate on documents, save documents online, set up groups and much more. Google Docs accepts many file formats, including DOC, XLS, ODT, ODS, RTF, CSV and PPT. As above, usage is free.
iWork 08 by Apple is the final alternative that I'd like to mention here. It costs $80.00 and is available now. The suite of products includes Pages that is compatible with Microsoft Word ( the 2008 edition), Numbers that is compatible with Microsoft Excel and Keynote that is an alternative to Power Point although it is compatible with Power Point in many ways.
Of the three mentioned, I can't really recommend one over the other although I would lean towards iWork 08 for one reason, it's an Apple product and it's supported by Apple.
Apple has one of the highest customer satisfaction ratings, if not the highest, for customer support.
Since iWork 08 is an Apple product, users can depend on that support to get the most out of their software.
Erik