LaCie's Wuala, online backup service added a new feature "Folder Sync," that let you synchronise files "online" as well as across multiple computers running Windows, Mac OS and Linux. Synchronisation will work both ways, with file updates automatically uploaded to cloud and synchronised with other PCs linked to your account. If you wish to revert to a previous version of the file, the company is also offering file versioning and "time travel" features to allow you to access and restore a previous copy of the file.
Wuala Pro starts at 19 Euro per year for a 10GB account, with accounts up to 100GB available for 99 Euro. If you don't want to pay, account upgrades are also available by donating part of your locak storage to Wuala's distributed cloud.
More Info: Waula