My Trek 7100FX came with a suspension seat post. The seat and post was stolen and I replaced it with a rigid pole on advice from the LBS. I chained the new seat to the frame so next time my entire bike was stolen. My replacement bike had another suspension post so I've been from suspension -> rigid -> suspension.

Initially after transitioning from suspension to rigid I could feel it. Prolonged rough terrain became uncomfortable much quicker (though my wrists give in much sooner than any other body part these days).
It wasn't too long before I stopped noticing (or perhaps just remebering what it used to be like).

I haven't really noticed much, transitioning from rigid to suspension, excpet it squeaks annoyingly as I go over bumps.

I don't think there is too much in it - I'm not bothering to replace my current post but I probably would buy a suspension post either.