I just gave Google Docs a try. This was almost an year ago. I didn't like it. It had lots of bugs. The formatting didn't work perfectly always, and the feature set was completely bare. I wasn't a hardcore Google user at the time, so I didn't stick around for long, and switched back to Office.
I don't have Office 2007 or 2010, just 2003, which I don't like at all. I started using OpenOffice, which has now become a lot better than MS Office 2003. But I thought, randomly one day, of giving Google Docs a try. I did, and I fell in love with it. Here are some things that I really liked about it.
Browser based
Being able to run from just a browser is a strong feature. I don't need to download anything at all, unlike other (even free) office suites. I just need an Internet connection and a web browser. It's a complete web-app. Period. This makes it run from any computer in the world. Almost. So no matter where I am and whose computer I use, I always have complete access to Docs, unlike MS Office, OpenOffice or Symphony or whatever.
Google product
This advantage may not apply to everyone. But I love Google and all the products. I use Gmail, Google Calendar, Blogger and whatnot. So having a complete office suite, that runs on any computer, all connected to my Google Account is an neat idea. No matter what Microsoft does, I am not looking back. Google offers everything for free.
Feature rich
Just months, ago, Google Docs wasn't very useable. I have experienced it myself. But now, it has so many awesome features. There has been an addition of web fonts recently, which lets you use newer fonts like Calibri, Cambria, Droid and more. There is a full blown equation editor, heading formats, and everything.
Still, the interface is very clean and slick, unlike the crowded and unorganized one on OpenOffice. [I don't say unorganized for MS Office, because in the newer editions, the new ribbon interface is really good.] Docs lets you do practically everything that you could do on another office suite, including export in various formats, which brings me to the next point.
Compatible
Docs is perfectly compatible with almost all popular formats. It exports your documents, spreadsheets, presentations and all in MS Office formats, Open Document format, and even PDF, which is really good. You don't need to fix up the teeny tiny errors or formatting issues that come up when you view your document in another program before printing. Just download it in PDF format, and it will work practically anywhere you go.
In the cloud
Around the time I am writing this, I am also writing another series on this blog, about moving to the cloud. If you have read the previous posts in it, you probably know that I am slowly migrating to the cloud. And it's a great thing that Docs is a web-app. All my documents are safely stored online, and I can access and edit them, or even download them from anywhere in the world. There's also a web clipboard, so that I can even paste the last cut or copied text from any computer, anywhere, thus continuing where I left off.
Mobile support
This one does not fully apply to me. But Google Docs has pretty good support for mobile devices too. I can see most of my documents on the go. If I had an iPhone, iPad (which has a special site for Docs), iPod touch, or an Android phone or tablet, I could even edit the files on Docs, straight from the browser. Moreover, iOS and Android users can even view PDFs and other file types that are not supported on Symbian and other OSes, right from Google Docs.
Free
This is one of the biggest ones. Docs, just like most other Google services is completely free. There is a 1 GB limit to your files stored online, which is negligible, as only the documents in formats other than Google Docs formats count. When you upload, you can convert your document or whatever to the Docs format, and when downloading it, you can simply export it as a PDF or whatever office format you require. If you require extra space anyway, which is rare, just pay the small amount. Rest is free.
Regularly updated
Microsoft does keep releasing regular security updates and other stuff, but Google Docs actually updates very regularly, being a web-app. There is no download required, so it is very easy for Google to deploy updates. There is always something new in every few weeks. I mean, actually, visibly new. Be it a new look, better interface, or just a new feature, such as new fonts. Microsoft doesn't provide such updates so frequently, if at all.
Though there are so many good things in Docs, it does have some problems. It could use some more features. It isn't yet comparable to MS Office, but can be a good substitute for those who like it. For myself, I'll be really happy to switch to Microsoft Office 2010, as it really helps in making better presentations and documents, and is slightly more user-friendly, but until then, I won't switch back from Docs anytime soon.