I'm curious, is work underway to see similar gains made in the I/O manager on Windows?
Does Windows provide a similar construct as 'select()' and also something equivalent to the newer epoll/kqueue systems, such that boosting the I/O manager on Windows will be rather trivial, or is the Windows I/O subsystem so different that the GHC I/O manager must be designed completely differently on that platform?
I do hope that someone more familiar with Windows takes up the torch.
(a) is a big deal because it makes it very easy to reason about what your program does, which is handy because (b) is the opposite :-) but makes certain kinds of computations very elegant to express.
 Not quite true but close enough
Quite separately, runtime and library performance for some kinds of parallel programs is better.
Both sequential and parallel code got better, for different reasons.
That all happens before getting shunted off to LLVM, which in turn does a lot of block-level changes (which particularly affect numeric code).