UPDATED 2010-05-27: See end of post for more correct fix.

Over time, my laptop has accumulated many programs, configuration files, … So after some update (I believe the Ubuntu 10.04 beta one) I noticed that all my Qt applications were using a different cursor theme. From the looks of it, it was relying on settings I had once set in my days as a KDE user/try-er.

Simply deleting the .kde or .qt folders did not seem to do the trick at all and people kept referring to kcontrol (darn Google’s old results for my queries) to fix it. However, that was not an option.

$ sudo apt-get install kcontrol
[sudo] password for ward:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package kcontrol is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  kdelibs4c2a kdebase-workspace-bin
E: Package kcontrol has no installation candidate

After some searching, it turns out the application to control KDE with nowadays is called systemsettings. So I quickly issued

sudo apt-get install systemsettings

fired up the program and fixed my non-matching mouse cursors.

Might I suggest the oxygen mouse cursor theme?

UPDATE:

As a sort of follow-up to this post, it seems I was mistaken. Meaning, my fix did work, but failed when X restarted. Not very handy thus. However, there is a permanent way (as far as I can tell). Open a terminal, issue

sudo update-alternatives --config x-cursor-theme

Then pick the cursor you want. This fix should be more eternal than the one outlined earlier.