Recover from invisible mouse due to misconfiguration
The linked wiki page describes a scenario whereby a misconfigured monitor width and refresh rate causes the mouse cursor to be completely invisible. Fortunately, it was possible to login (ssh, actually) as another user, and manually edit the configuration file. In that case, I was fortunate that I knew the exact time of when the problem started occurring, I had a working user, so I simply had to compare files changed at that time, between the working and non-working users.
KDE/X.org should allow the user to recover easily from such misconfiguration.