In my quest for the perfect sync for the relatively small set of sensitive files I want available from all my workstations I've tried several cloud based services: Dropbox, JungleDisk, Wuala, and Egnyte just to name a few.
Dropbox and JungleDisk both require custom-rolled workarounds (like using a TrueCrypt volume) to keep sensitive files secured. Egnyt encrypts your data at rest but they use a common key which means you are reliant upon their business practices for data security. Wuala encrypts your data with a private key before transmitting it, but their client is quite cumbersome. I've found SpiderOak to be the best fit for my needs.
- Native Mac client that starts automatically and runs quietly in the tray
- Zero-knowledge encryption of all my files
- Supports a smart folder sync
- Free entry-level account with 2G of space