ubuntu upgrade vs dist-upgrade

• apt-get dist-upgrade (smart upgrade in Synaptic):

this command upgrades packages trying to satisfy the dependencies in a "smart" way -- that might mean removing packages. It is not recommended to use it if you don't know exactly what you are doing.

• apt-get upgrade (default upgrade in Synaptic):

this command upgrades only the upgradeable packages, it doesn't remove packages. From man apt-get: "New versions of currently installed packages that cannot be upgraded without changing the install status of another package will be left at their current version."