Yes you are right but Google/Amazon are read-heavy so a big hash table works perfect since there is less disk access - however FaceBook is both READ and WRITE heavy so its more challenging. From their last SIGMOD Cassandra paper, I gather they use some sort of in-memory write which is then synced with their bigtable. Very cool stuff!
I worked at a big tech company doing SemWeb, where my experience was exactly the same. Everyone was scratching their head.
Now I've moved into Healthcare IT environment, where SemWeb makes perfect sense. Its like the best tool for the job.
The essential difference is what end of the stick you are picking up. The tech folks who are trying to shoe-horn RDF/OWL onto anything n everything (e.g. search) are failing. On the other hand, Healthcare/Life science folks who have to work with heavy knowledge intensive stuff, its working like a charm.
The SemWeb story is quite similar to Amazon Kindle.. wherein the tech folks are hating it whereas real users are all over it.. So it might seem like a failure to all you tech bozos.. but the domain experts are lovin' it.
So you think that money is the root of all evil. Have you ever asked what is the root of money? -- Ayn Rand
