I've just got rid of a suspension seat post on my old 2000 aluminium frame Cannondale Hybrid; primarily because it was old with quite a lot of sideways play and it was just heavy. I replaced it with a light Thomson in-line seatpost; possibly an error as it moved the saddle position very slightly forward, although it seemed OK when I set it up (height and front/back position). I do an 18 mile (one way) commute once or twice a week (train on the other days) on cycle paths and I certainly noticed the loss of the suspension post on the bumps. I woke up one morning with what felt like a whiplash injury and cast an accusing eye at the bike. The snag is, just before the seatpost change, I fitted carbon forks (prev steel) and new stem etc as the old headset was worn out with the old stem siezed to the forks. The LBS reckon they got the set up pretty close to the old stem which was an old adjustable version (also heavy). I also put new narrower higher pressure tyres on as well. I'm not sure whether I should have used a set back seat post, but then being slightly more upright should be better for your neck, or the loss of the suspension post has meant that I'm feeling all the bumps. Although I'm really pleased with the new front end changes, I'm not sure they might also be contributing. I'm inclined just to stick with things for a while and see if I just get used to the changes for fear of running up a huge bill buying different components. I've read that being too 'laid out' on the bike is tough on your neck, but then being too upright means your spine takes all the shocks. Being an old aluminium frame it's going to be a 'hard' ride anyway.