How can I install Ubuntu One in Kubuntu?
There is a project (as @Rinzwind indicated) on Launchpad which looks like it attempted to produce a native KDE client - It was part of the Google Summer Of Code project.
Unfortunately, the associated PPA has been removed and the alpha-software which exists as a tar file has not been updated since August last year. The assumption therefore is that the project is either in an extensive lull or has been abandoned.
The software itself in the tar file I have found nigh-impossible to compile.
My suggestion therefore would have been to install
However this package is only available for Maverick and Natty. It hasnt been backported to Lucid. There is one potential PPA available with this package backported. However, as the author himself says - use with care. Therefore - take the authors advice and backup first using a good backup tool such as Clonezilla
To Install on Lucid/Maverick
NOW VERY IMPORTANT
Open your software sources and untick both the Kalon33 experimental PPA and Kalon33 PPA. The reason is that you probably will not want any of the authors extensive builds for Lucid/Maverick.
Finish off running
The package will install Ubuntu-One under the Settings menu.