On our robot(s) we have changed a brass bushing into a Delrin one, We have also "Swiss Cheesed" the <edit>ROBOT</edit>!
It all depends on how much weight you need to lose as well.
We are going with the slotted idea to reduce weight on our side panels, instead of a bunch of holes.
NOTE:
MAKE SURE YOU FINISH DESIGNING YOUR ROBOT BEFORE REMOVING MATERIAL!!!
Last year we jumped the gun on machining holes and accidentally machined a spot where a future mechanism sat. We had to weld a panel in the spot we machined,

Not a fun thing to do!