If you use Windows and do a lot of work with other people (or need to sync information between multiple computers), you should definitely check out Windows Live Mesh.
It’s incredibly flexible…I sync folders between 3 computers and have access to all of the files via a browser as well.
What’s more, you can invite others to have access to individual folders very easily.
So, I have one folder which I share with my assistant, Mary (she’s virtual) and I have another folder for the 8 people around the world participating in a Microsoft-funded project.
It’s a critical part of my infrastructure and I highly recommend it.