Do not grease a carbon post, just don't do it.

You can use sommat like Tacx Carbon Assembly Paste if they slip, but I've always put them in dry.

Titanium is more bendy, carbon absorbs high frequency vibration.

I genearlly don't listen to people that say they can tell the difference with a carbon post off road, there's just so many bumps and things going on for it to make much difference! They won't snap unless you're really fat/have no technique/buy sommat cheap.

If you want shock absorption buy a suspension post.

i changed from an alloy post to a raceface Next carbon post on my inbred and it made a significant difference to sharp vibrations through the seat.

 I noticed that when i hit sharp angles or roots i was still bounced by the movement but i wasnt jarred by the shock, much less fatiging over a long xc ride.

my riding  buddy says he can see it flex when he rides behind me but i havent had any reliability problems and had it a couple of seasons. 

I run an easton carbon step, It certainly does take a little bit out of the bumps, As Ben says it just takes the jarring effect out of them.

I'm 14 stone and sometimes heavy handed and its never caused me any probs..