What about Redland? It seems to have good SPARQL support and it's got bindings for every language under the sun.
I've been playing with ActiveRDF in Ruby. It's very well polished, and having a uniform interface to different triplestores is really nice, but the lack of support for things like blank nodes is frustrating.
Your blocks idea is very interesting, but I'm having difficulty seeing what data connections can be made between Flickr or Twitter or Myspace and dbPedia or ...
