Alrighty, I'll try to keep this simple.
(Running 5.1.1, by the way)
I can't see my mouse cursor!
I can left/right click normally, stuff hilights when I mouse over it (so I can kinda tell where it is), the scroll wheel works, I just can't see it.
Everything's fine on the same machine under 5.0.1.

Extended details:
I think the problem is with X; since the lack of cursor includes the checkerboard grey screen with the "X" cursor that shows right as it starts. No cursor there, either.

What part of which configuration file do I have to tinker with to fix this?
The only workaround I've found so far is to create a persistent home under 5.0.1, then load it (and its system config) under 5.1.1. Cursor works fine then, but lots of other things (like synaptic and Iceweasel) break because their configs have changed.

TIA!