There is a Lucene index in http://repo1.maven.org/maven2/.index/, and it is the index of Maven repository. it can contains a lot of information about artifact even class names in jar file. I thin Maven plugin can use this index to implement following features:
1 artifact search
2 code completion for groupId, artifactId and version
3 add artifact quickly
It is easy to create new plugin to implement such features, but if is supported by default, and it will be very useful.
Please visit http://docs.codehaus.org/display/M2ECLIPSE/Nexus+indexer for information.