I have been using Wuala for quite a while. The great thing about Wuala (as opposed to Dropbox and other competitors) is:

1. that you can earn storage
2. that all your data is strongly encrypted

In order to earn storage, you dedicate a part of your own hard disk space to Wuala to store other peoples cloud data (called "trading"). For this to work, Wuala has to run all the time. But when I log out from my account, the Wuala client is closed and trading stops. There is a nice post on the Wuala blog that describes how to run Wuala as a daemon, that earns you storage capacity also while you are logged out:
Effective usage running Wuala on Debian.

For some reason google doesn't easily find this blog post. Therefore here the short version of how to start wuala as a daemon:

login wuala
screen wualacmd
Ctrl+A+D
wuala connectionCheck
wuala login username password
wuala startTrading