According to the site "Wuala protects your privacy: In stark contrast to most other cloud storage services, all your files get encrypted on your computer, so that no one - including the employees at Wuala and LaCie - can access your private files. Your password never leaves your computer."

I think Hushmail made the same claims, until compelled by law enforcement to send altered client software to the machines of suspects.

Not sure how these other companies operate, but unless the user hand-encrypts files with openssl, gpg, pgp, etc., then the trusted client software has the potential to be a vector for compromise.