Not affiliated with them, just looking for some HN feedback. To be honest I was surprised this didn't come up on hnews before - or at least my googling wasn't turning up anything. There's also secretsync which I believe is the precursor to this.
There's also Boxcryptor which looks similar though I haven't tried it yet. I've been wanting to use one of these encryption services but I'm also wondering what people think of them.