I've run into this in Xubuntu, I can only assume (K)Ubuntu would behave the same as for obvious reasons I'm not going to test it there.

When you fill up your entire disk space and try to delete something you get an error message because since there is 0 bytes free the system cannot move files to trash. AFAIK there is no easy way around this in the GUI, so a beginner will be stuck. It would be great if in such a situation the system would offer to remove the files directly, forgoing the trash. Of course this should not be done automatically, rather a yes/no dialogue should be displayed.

PS. In case anyone wonders how can this happen - a small HDD plus the fact that Add/remove programs does not check whether the required disk space is available...