I've used wuala for linux and have found it quite rough around the edges.
* not completely decentralized or open source. If wuala goes out of business, your data may not be recoverable.
* web interface is lacking (poor folder navigation/listing)
* doesn't work without X on linux
* even with X, not all features are available through the command line or API, though some are
* the interface that is provided is clunky
* the status messages leave me wondering where in the process an update is. If a piece of software can't reliably tell me where it is in a process, I can't trust that the process is happening the way I expect.
Yep, Wuala is not completely open source and it is a business. Your worry that they might go out of business soon is mitigated quite a bit by the fact that they have been acquired by LaCie  over a year ago.
I suppose Linux definitely isn't their main market and while the Web Interface is lacking at the moment they are working on an overhaul.