I'm currently using wuala for remote storage / sync, and while I dislike their GUI greatly (and their poor support for headless systems), they have one amazing feature where a virtual disk (windows) or mountpoint (using CBFS on Linux) is created letting me keep my files stored remotely but access them as though they were available locally.
I haven't found any free way to do this with any of the other major providers (DropBox, SpiderOak, etc), but I'm wondering if anyone else has seen anything?
A raw S3 storage solution is available using S3FS (http://code.google.com/p/s3fs/), but it's missing two important features: automatic sync of local files (because sometimes I do want a local mirror) and more importantly, a windows version (I can't seem to get it to compile using Dokan).
Has anyone found any alternatives to Wuala for this purpose (using either FUSE, WebDAV or anything) which supports both Windows and Linux?
JungleDisk does this on Windows and Linux, providing a shared network drive that's mapped onto Amazon S3 or Rackspace Cloud Files, and also acts as a cloud backup service. It caches some files on the local disk so the network drive is not always as slow as the cloud storage service.
JungleDisk does have some known security problems - in particular it uses an MD5 hash within its encryption architecture in a way that makes it very easy to decrypt its data if you have a weak password.
However, the Dropbox model has much to recommend it - your Dropbox folder is a "100% cache" of the remote files, so they are available offline. You can handle them just like other local files (e.g. file change notification tools work as normal, and they can be backed up with normal backup tools if needed). Dropbox has a headless install method for Linux and its Linux client has been kept up to date for some years now.
I did find that very large files (600 MB, CD sized) sometimes never uploaded to JungleDisk - that was a couple of years ago so maybe it works better now.
The main benefit of the "remote files only" approach as in JungleDisk is if you really don't want a local copy of the files, because they are very large or there are confidentiality issues with local copies.
With Microsoft SkyDrive, you get 5GB free and you can download the Windows Live Mesh client that supports file synchronization to SkyDrive.