This thread was mentioned in a performance sub-group posting. Give it a read.
Back? It means, so far as I can see, that PG is toast. It will fall down to being the cheap and dirty alternative to MySql, which even has, at least two, multi-threaded engines. DB2 switched it's *nix engine to threads from processes with release 9.5. Oracle claims it for releases going back to 7 (I haven't tried to determine which parts or applications; Larry has bought so many tchochtkes over the years...). SQL Server is threaded.
Given that cpu's are breeding threads faster than cores, PG will fall into irrelevance. Too bad, it's kind of a nice database.