Lucene has two Google Summer of Code students!
The first project (LUCENE-3312), proposed by Nikola Tanković, will separate StorableField out of IndexableField, and also fix the longstanding confusing trap that one can retrieve a Document at search time and re-index it, without losing anything. It's unfortunately not true!
The second project (LUCENE-3892), proposed by Han Jiang, will create a postings format using PForDelta compression (PDF). Long ago we saw great performance from PForDelta, but with a hacked up prototype patch that couldn't be committed. The goal of this project is to implement PForDelta "for real" and characterize the resulting performance.
Welcome aboard Nikola and Han!