Checks on .changes files:

 * mandatory fields: "source", "binary", "architecture", "version",
   "distribution", "maintainer", "files", "changes", "description".
 * format of maintainer field is valid rfc822/2047 compatible.
 * closes field contains only numbers.
 * files field not empty.
 * check for a valid urgency.
 ...

Checks on .deb files:

 * check that it is an ar archive.
 * check that it has exactly 3 chunks (although this may change once signed
   debs are accepted again).
 * check chunks are exactly: debian-binary, control.tar.gz and data.tar.gz.
   (or data.tar.bz2 if there's a correct Pre-Depends on dpkg, in the future
    data.tar.lzma will be added).
 * check for mandatory fields in the binary control file: "Package",
   "Architecture", "Version".
 * check that the package name matches the one from the .changes file.
 * check if the package name is valid. (as defined in the Debian policy)
 * chack if the version is valid. (as defined in the Debian policy)
 * check if it's a known architecture.
 * check for an empty depends field.
 ...

Checks on .dsc files:

 * check for .changes files with multiple .dsc files.
 * source uploads must contain a .dsc file.
 * check for mandatory fields: "format", "source", "version", "binary",
   "maintainer", "architecture", "files".
 * check if the package name is valid. (as defined in the Debian policy)
 * chack if the version is valid. (as defined in the Debian policy)
 * check for an incompatible version in the format field produced by a
   broken dpkg version.
 * validate maintainer field.
 * validate build-dependecy fields.
   - check for invalid fields produced by a borken dpkg.
 * check that the source can be extracted.
 [ The following two are using by the version tracking stuff...]
 * check that the changelog exists.
 * check that the changelog format is parsable.
 ...

Checks on files:

 * check that the filenames are correct.
 * if the section is byhand send to the byhand queue.
 * if there's a .deb, check if the control field can be opened.
 * check md5sums.
 * check for a valid timestamp.
 ...