Very fast, very easy. I have been checking this out the past few days and I like it-- Have yet to move any of my actual project teams over, but I intend to try. I have used zoho, google docs, and huddle in the past. Currently using Huddle for its LinkedIn app, but this puts all of these to shame with simplicity and usefulness.
Google should buy it for Docs - looks like it was designed with their API. The help page (Learn more) is also a model of clarity and good documentation. Excellent work.
I'd really like the ability to share access with my cofounders. Without that one of us ends up being a choke point.