Very minor, largely cosmetic nits:
According to Lee, that the pom templates are static- and don't update versions with ivy, used for versioning dependencies elsewhere- is by design for this pass.
I agree that adding the javadoc and sources jars can be pushed to a separate issue (since this will also need to happen on trunk). The changes complying with maven naming conventions require that this be marked as an incompatible change (the build now generates hadoop-<name>-<version>.jar vs previous (hadoop-<version>-<name>.jar), so this needs a release note calling that out.
Other than these, the patch looks good and its effect in staging has been confirmed by members of the Mahout team (thanks Benson and Sean), and it worked for the 0.20.2 release. Thanks, Giri; this is excellent.