That would be cool. I'm not sure it would change much though. I know someone working with search data who recently tried out Neo4j with a test data set of 500,000,000 nodes and apparently was really disappointed with the results.

I'm not sure that graph data (generally) is particularly amenable to being spread across multiple nodes. My understanding is that ArangoDB has implemented some clustering based on Googles Pregel Framework, so I suspect it might fare a bit better in my friends test... but in spite of my urging I don't know that he has had time to recreate the test with Arango. I'm keeping my fingers crossed.

I don't know if any database is fun to deal with at that size. My experience with Arango has been an unremarkable amount of remarkably complex data, so I would also be interested to see the results with something huge.