I won’t be surprised at all if the whole multithreading idea turns out to be a flop, worse than the "Itanium" approach that was supposed to be so terrific—until it turned out that the wished-for compilers were basically impossible to write.
Let me put it this way: During the past 50 years, I’ve written well over a thousand programs, many of which have substantial size. I can’t think of even five of those programs that would have been enhanced noticeably by parallelism or multithreading. - Donald Knuth

Concurrency is the next major revolution in how we write software
Applications will increasingly need to be concurrent if they want to fully exploit continuing exponential CPU throughput gains. - Herb Sutter

these libraries are almost universally C libraries and require careful use in C++

opinion seems to be divided

in windows, probably yes. threads have been widely used over the years.
in unix, probably no. fork is very efficient.
fork is very efficient.

most of the push towards concurrency seems to be in the kernel (solaris, bsd), filesystems (zfs) and libc ( bsd's gemalloc, google's tcmalloc) right now.

I know that important applications for parallelism exist—rendering graphics, breaking codes, scanning images, simulating physical and biological processes, etc. But all these applications require dedicated code and special-purpose techniques, which will need to be changed substantially every few years.