Comment 63 for bug 1265192

The partitioning step of the Kubuntu installer is more detailed (and less ambiguous).
It displays the resulting partitions for the selected option graphically.
The options also appear to be a bit more detailed and less ambiguous.

Maybe you should consider using this, or part of this, in the Ubuntu (and other flavours) installer (it's still ubiquity, right?).
It appears to be a lot less ambiguous, but a bit harder to understand by beginners (but if it saves them from losing data...).