The ones that have upgraded to Snow Leopard first you will have to deal with a dark screen right after the instal is finished (only on MacBook Pro) it seems.
The work around is to access your machine via remote desktop or share screen facilities. Once the machine reboot you should be able to increase the screen brightness from the keyboard buttons. The other solution is to use a normal Flash Light and point it towards your screen, this will allow you to see where you want to click (strange but true).
The other annoying thing you will want to change is the nasty blue shade/border around the windows when in Exposee.
This is the way to change that:
System > Library > CoreServices > Dock.app
(right click: Show Package Contents)
then Contents > Resources
The images are: expose-window-selection-big.png for normal windows and expose-window-selection-small.png for minimized windows.
Having the image the same size and making the visible part smaller reduces the size of the highlight and the other way around.
Now you choose what you want to change it to.
There is a nice Tutorial and a Zip File Right Here