I've become an ardent Google Documents fan over the past few months -- especially as its support for Safari has improved (didn't say perfect; just improved). I use it for collaborating with clients and 43f guest authors, as well as for managing small projects and keeping various small teams organized. Personally, I find it simpler than a wiki and a lot more powerful than using a static .doc.

My favorite use right now is to use a single shared document as a common space that 4 or 5 people have access to and that they can use to give each other to-dos, ask questions, etc. I know stuff like Basecamp does this better and certainly with more sophisticated features, but I'm really attracted to the simplicity of the one-document approach -- especially for informal, remote teams.

I think my gDocs cincher was the first time that it occurred to me to see if I could even look at my documents on my iPhone; I was gob-smacked to see that it actually worked. Obviously it's not optimal for doing lots of editing, but you can see and perfunctorily edit your documents without a laptop, and that's just pretty mind-blowing to me.