For a new project which uses Maven I would like to add distributionManagement configuration in the pom.xml which will connect the project with the Sourceforge.net file upload system.
I have found this information (of 2007), is it still valid or do you know updated resources?
http://docs.codehaus.org/display/MAVENUSER/MavenAndSourceforge
Related question: How can I deploy artifacts from a Maven build to the SourceForge File Release System?
This looks correct. However, note that it only describes deploying the site artifacts, not the project artifacts (JAR and POM). And while it's possible that you could use maven to deploy your artifacts, I'm not sure that you'd want to -- the Maven directory structure is different from the SourceForge structure (of one directory per release).
If you're looking to deploy your project releases to Maven Central, read this: http://maven.apache.org/guides/mini/guide-central-repository-upload.html
The process has changed in the last year or so. At one time you could request that your project be added to a nightly rsync job, but apparently now you have to deploy directly to a recognized repository. Given the number of times that rsync job would fail, it's no wonder they decided to change the process ...