Jon Nelson wrote:

That, for me, is the next question - how can one educate LVM about the
underlying block device such that logical volumes carved out of that
space align properly - many of us have experienced 30% (or so)
performance losses for the convenience of LVM (and mighty convenient
it is).

When you do pvcreate you can specify --metadatasize. It will add padding 
just to hit next 64K boundary.

So i.e. if you do

#pvcreate --metadatasize 256K /dev/sda

your metadata will have 320K

but with

#pvcreate --metadatasize 255K /dev/sda

it will have 256K

After that, lvm extents will follow - with the size specified during 
vgcreate. Also I tend to use rather large sized extents (512M), as I 
don't really need the granularity offered by the default 4M.