I am not opposed to the idea, and I am not condemning them. I just do not understand what they are for.
My take on suspension is that it is supposed to increase your control on the bike by keeping your wheels in contact with the ground. I can not see a benefit to a suspension seatpost other than comfort. as to the downsides they seem like they would add weight, and it also seems to me that you might get some bob under heavy seated pedaling. Although I have seen some pretty sweet bikes with the suspension posts on them (Buzzbomb's being the most memorable).
Can some of you suspension seatpost fans help me out? Do they add some level of control?
I ride a hardtail, and I am sincerely curious about them.