I was happy user of the iWork Suite 08 since I moved to OS-X. It somehow better matches the way I am thinking and does much better job than Office to get me from idea to acceptable looking rendering of that idea in the form of document, spreadsheet or presentation.

In past two month I was involved much more interaction with the requirements, business analysis and project management part of the process. Which inevitably means much higher exposure to documents creation, collaboration and exchange. iWork gives you reasonably good compatibility with Office document formats, which means that you can easily import almost every Office document modify it and export it back so that Windows user will see almost all of your changes. Almost everything will be just fine. Unfortunately, almost is not the same as everything: it often breaks fine details of formatting, reviewer comments and does not really work for more complicated Excel spreadsheets. Especially those spreadsheets which project manager-ish people so love to create.

I tried to use OpenOffice/NeoOffice which suffers from the same malady. It spoils different set of features than iWorks, quite often works well, but it cannot be trusted. On top of that, it just does not feel right and is kinda ugly.

So I had to take a deep breath and installed Office 2008. After few weeks, here is my impression and very brief comparison of all three mentioned suites.

With Office 2008, I was not having very high expectations regarding user experience on Mac and I have to report that Microsoft did not disappoint. I indeed was not too great experience, starting with installation.

Office 2008 contains 4 products. I absolutely wanted Word and Excel, was not quite sure about Powerpoint (because Keynote is sooo much better),  and certainly had zero interest in Entourage and Microsoft Messenger.
Guess what: Microsoft installer, as many times before, knew better what I want and did not give me a chance.  All questions asked were related to what Microsoft needs to know (serial number), with little regard for users interest.  It also installed whole bunch of fonts, which I did not really want - but I guess to provide 100 % compatibility with Windows, it may be a good idea to include same set of fonts as Windows office has.

After installation, Office 2008 works reasonably well. Minor annoyance is start taking forever - I guess it is because (unlike under XP/Vista) OS-X does not preload shared components (and does not eat up memory just to make Office appear start snappier).  As soon as any Office application is running, I have occasionally seen weird behaviour when switching between windows (note lowercase 'w') and does not play nice with Spaces. Sometimes scrolling forgets to redraw screen in word and you have to minimize/restore to get back to readable text. And it is generally quite slow even on very fast and powerful machine.

With respect to the main motivation for getting Office - seamless document compatibility - that problem appears to be solved. So far I have not seen anything that would be distorted or deleted just because I touched the file on the Mac.  Only exception is Excel - Office 2008 does not support VBA macros, so your mileage with more advanced spreadsheets may vary.

Should I mark my experience with Office 2008 using school grades, it would be:
- installation: C
- user experience: B-
- compatibility with Windows Office: B+
- price/performance ratio: D
- overall: B-

For iWorks'08 it would be:
- installation: B (if I recall correctly, it was OK, but required installer).
- user experience: B+
- compatibility with Windows Office: C
- price/performance ratio: A-
- overall: B

For NeoOffice:
- installation: C-
- user experience: C-
- compatibility with Windows Office: C+
- price/performance ratio: A
- overall: C+

Recommendation:

If you are working on Mac as part of a team that collaborates using Office documents, you most likely need Office 2008. Unfortunately the only office package that comes very close to be compatible with Office 2003 and Office 2007 is Office 2008.

If you value user experience, aesthetics and are OK with mostly one-way conversions between Windows Office, you will find iWork provides excellent value and will make you feel at home. If you never have to exchange documents with Windows world, enjoy it - we all who have to do it daily are green with envy.

If you for economic or ideological reasons refuse to pay for software (or only for software made by certain companies ;-)) - or if you require compatibility with Linux based office, you have no other choice than NeoOffice or OpenOffice. The first one looks considerably better on OS-X - although still not quite right.