Doug Cutting- the genius behind Lucene- put a proposal out for Google's Summer of Code for someone to build a GData server on top of Lucene. Interesting to see how this could turn into a pretty cool interface for Lucene. It's also a picture of how GData could and something that is a usable generic standard for search interfaces. I guess it would be comprable to JSR-170, if they added versioning...
Now...we just need GData support on the Google Search Applicance.
SummerOfCode2006 - General Wiki
The Google Data API extends Atom to present a simple, searchable database. A Lucene-based implementation could be provided as a Java .war file containing a few servlets.