+1 for some carbon posts being a big pain in the ***, even for 2-bolt. Be sure you can get infinite tilt adjustment. As for 2-bolt systems, be sure that the 2nd bolt is easy access if you don't have a cut-out saddle design.

+1 for Thompson aluminum seatposts. Plenty of carbon devotees love Thompson posts. Probably the best seatposts out there really.

If you don't have a torque wrench (I don't yet..ooops), my LBS gave me a good rule of thumb. Wrench until it's fairly tight and then back it off a bit. There's no need to really crank the clamp on there, ever. It's got to be pretty loose for the post to do any slipping. I used the same rule of thumb when I had to move my FD as the shop had it set up all wrong and even if I had a torque wrench I don't know what the torque ought to be at that part of the seat tube.