Eric Zeman recently posted about a failure of Google Docs, after over a year of using it with no problems. So what was the problem? Although you can export to a .doc or a .xls file, you can't export a powerpoint file. The presentation software only allows you to export a PDF or text file. I assume that support is coming, but it could be a dealbreaker right now.
I haven't used Google Docs a ton yet, but from what I remember, the word procesor and spreadsheet functionality has been there for longer than the presentation functionality. None of it is very advanced, but it covers the needs of probably two thirds of the users out there. OpenOffice is a step up, and MS Office is another step up. OpenOffice is probably good enough for 95% of the users, with only a small number actually needing MS Office. We won't go into the differences between Office 2007 and previous versions here.
The cool thing about Google Docs, however, is the collaborative features which are not present in other office suites. You can have multiple people editing the same document at the same time, and the changes that are made are logged. You can easily share a document with others to view or to edit, without ending up with multiple copies of your file sitting on email folders and saved random places on hard drives and USB drives. There's no question who's got the latest version.
Another feature of the presentations is that you can launch a presentation and then people can join in your presentation via the web and chat along with you next to the presentation pane. Add voice from Google Talk to the presentation, and you've got a sweet product. Actually, I'm hoping they'll add video to their Google Talk application as well so I can get off Skype.
I recently sat in on a presentation by a company Xapio that claims to have solved all of these problems with tracking versions of documents and who has read or otherwise accessed them. However, all their product consists of is a special mail server that strips out attachments, saves the attachment on their server, and sends the link. They can then log who downloads the file using that link. That's nice, but you still end up having to download the file and work with it on your local machine. What if you have a bunch of people working on a document together? You'll have all the versions of the file saved on their server, but only if they have been emailed back and forth. They were doing some cool things with protecting confidential information from going out via email, and the lawyers will love that you can log whether or not someone has read a document you sent them, but it's not really collaborative.
Microsoft is so far missing the collaboration boat as well. They have Sharepoint, but it suffers from the high cost, confusing licensing terms, and of course the security and administration headache that comes from using MS products. Sharepoint has real-time presence information, wikis, blogs, calendars, document collaboration features, etc. Some large enterprises with large IT budgets are obviously going to be better off using Sharepoint, but small companies, nonprofits, students, families, etc. can have pretty much the same thing using free tools hosted on a server they don't have to manage.