Lambda the Ultimate

Large Scale Graph Computing at Google - on the official Google Research blog.

Here is an extract -

... we have created scalable infrastructure, named Pregel, to mine a wide range of graphs. In Pregel, programs are expressed as a sequence of iterations. In each iteration, a vertex can, independently of other vertices, receive messages sent to it in the previous iteration, send messages to other vertices, modify its own and its outgoing edges' states, and mutate the graph's topology (experts in parallel processing will recognize that the Bulk Synchronous Parallel Model inspired Pregel).

I wouldn't say this is directly PLT related, but it is a parallel programming model - compute-communicate-synchronize-loop - that is probably of interest to language buffs from the DSL angle, like the GPU programming models.