BitTorrent Sync although still in Beta offers a App and protocol for DropBox like file syncing. As it is an app rather than a service you use you own disk space. Hope fully it can also be run on webfaction to setup a private cloud.
The advantages I can see are:
- Private Storage - Secure, third party can not be forced to hand over data if hosting it on own hardware.
- Private Storage - Unlimted space, Dropbox give 2GB free basic webfation account has 20-40Gb storage. S3 offers very cheap way to scale for cloud storage. Synced from home computer TB available.