I've always used Google as a search engine: I can say that having tried out all its competitors it's results are simply the most relevant.
Then about half a year ago I decided I needed to keep my bookmarks synchronized between my laptop and desktop, and Google Browser Sync was just the thing for me and has worked perfectly.
Two months later I got fed up with only being able to check my RSS feeds on my desktop and moved those to Google Reader instead of Desktop Sidebar.
Now, about a month ago I got fed up with all the spam that was getting through Thunderbirds mail filters and switched to Gmail, uploading all my existing email archives at the same time with this tool. I then had much less spam, a much better ability to organize my mail, and the ability to get my email anywhere.
Then a week ago the link at the top of Gmail to Calendar lured me in.. now I depend on Google Calendar utterly to keep track of all the stuff I need to do that I used to keep around on bits of paper I would carry with me.
Two days ago I bit the bullet and made iGoogle my home page. I can now get my email, calendar and TODO items (which I used to keep written on the back of my hands!) from the moment I start a web browser.
And it's only this afternoon that I realized how much my life had come to depend on these guys. It's actually fairly scary how much damage they could do to me if they decided. But I'm now way too dependent on their integrated suite of tools for it to be worth my while to do anything about it. I really feel like I'm waking up to a web in a way I haven't really felt before, despite having used it for donkeys years and I'm sure that the masses who are as Google-agnostic as I was just over a year ago will start down the same path once they begin to own multiple internet connected devices and require ubiquitous data access.
I've ridiculed it in the past, but maybe they are on to something with this online office suite idea after all..?