Since Debian Lenny went final a few days ago, the sid/unstable repos are just that ... unstable.
Please use your common sense when dist-upgrading, make sur you read the messages, whether using smxi, apt-get or synaptic, otherwise you may find your system hosed.
You may wish to wait a while until sid 'settles' down a bit.
Use the sidux forum to see if dist-upgrading is advised against at a particular time.
Note this is particularly true for antiX users using the sid repos, but even in Testing, there may be some problems.

