EDIT: It turns out the article does talk about process migration, but still doesn't answer the distributed computation question.
"Process migration is also deliberately absent from Plan 9. Although Plan 9 makes it easy to instantiate processes where they can most effectively run, it does nothing explicit to make this happen. The compiler, for instance, does not arrange that it run on the CPU server. We prefer to do coarse-grained allocation of computing resources simply by running each new command interpreter on a lightly-loaded CPU server. Reasonable management of computing resources renders process migration unnecessary."
EDIT2: Ah, there's no automatic thread distribution. But you can fake it but forking multiple processes on multiple CPU servers and sharing their address spaces. Does this mean you have to write your own CPU server allocator?
"Plan 9 does not implement lightweight processes explicitly. We are uneasy about deciding where on the continuum from fine-grained hardware-supported parallelism to the usual timesharing notion of a process we should provide support for user multiprocessing. Existing definitions of threads and lightweight processes seem arbitrary and raise more questions than they resolve. We prefer to have a single kind of process and to permit multiple processes to share their address space. With the ability to share local memory and with efficient process creation and switching, both of which are in Plan 9, we can match the functionality of threads without taking a stand on how users should multiprocess."