Incoming is the directory new packages are uploaded to before being added to the Debian distribution.
Packages in Incoming are totally untested (except possibly by the package maintainer) so it is possible that they contain packaging errors or bugs in executables that could render your machine unusable. In addition, the files in this directory have not been checked by md5sum or pgp to verify that they are intact or were uploaded by a registered Debian developer. You can, however, get the devscripts package and use the dscverify script to check the basic validity of a package.
We recommend that Incoming NOT be mirrored. For access to the Incoming directory, use http://incoming.debian.org/
You have been warned.