I had heard about them but never had taken a good look. Now I did and choose not to deal with them. Some quotes from their website:
> certain crypto actions (signing and decrypting) are limited to users who store client-encrypted copies of their private keys on the server
No. Especially combined with the next one:
> On the website, all crypto is performed in JavaScript, in your browser. Some people have strong feelings about this, for good reason.
The second sentence sums it all up.
I think the service has been made with good intentions, but the pavement on the road to Hell...