http://jeremy.zawodny.com/blog/archives/006687.html
Here is a good blog entry with a talk on GData from someone who worked on it. The only thing I think Solr needs is faster replication, which perhaps can be done faster using a direct replication model, preferably over HTTP of the segments files instead of rsync? Reserving rsync for the optimized index sync. The only other thing GData does is versioning of the documents.
