Should I oil my seat post?
Greasing your seatpost will prevent problems like this:  "Removing Seat Post rusted into downtube".

Don't use chain oil, grease is what you want.  As whatsisname pointed out, all fasteners on your bike should be lightly greased.  This is what keeps them from corroding and seizing over time, becoming a real pain to remove.

If you have trouble with a slipping seatpost (like me), carbon grease is what you need.  Contains enough grit to keep from sliding, while still offering protection.