At 2hD we work in close collaboration but generally a couple of thousand kilometres apart. While the gap between us can come and go, the work needs to flow on a seamless basis. We mash together a number of technologies to achieve this, but one tool has really helped us to crack our file sharing issues: SugarSync.
It is a cloud based backup that allows a fairly fine-grained control over which files get synced to where. We think it is, well... sweet.
If you would care to check it out, we can both benefit from free storage — 500 mb each if you sign up for a free (5 Gb) account, and 10 Gb each if you decide to move up to a paid account. Just follow this referral link. Sweet syncing!