It's Stuck? Whaddya mean it's stuck?

For some chemical reason, carbon fiber likes aluminum. Aluminum seatposts can run the risk of seizing to a carbon frame, and vice versa. When left in contact for a long period of time, carbon and aluminum will bond together making seatpost adjustment difficult if not impossible.
One easy way to prevent this is to ride a seatpost that is the same material as your frame. If you are particularly loyal to your Thomson seatpost and carbon frame, just check up on it every couple months. Applying a smear of grease to the clamped section of seatpost should prevent seizure without compromising the stability of the post.
Carbon bonding with aluminum isn't necessarily common, but it happens. If you're carbon bike has been sitting for a couple of years and you can't adjust your seatpost, hope is not lost. You're probably going to have to pull that bottom bracket out and see if you have a hollow seat-tube (Bianchi is a popular brand which often doesn't). If so, make sure the top end of you seatpost is fully sealed (if not, plug up the hole), get a can of Coke and pour it down the seat-tube and let it sit overnight. Seriously. I don't know much about chemistry, but there is something in carbonated sodas that loosens up seized parts. Just be careful once you get the seatpost to budge that you don't get coke all over the place, and flush it out thoroughly with some sudsy water so you aren't wondering where all those ants are coming from next summer.