In my (bitter!) experience:

product manager=somebody who doesn't want to

program anymore and probably was never that good

at it - wants to set the agenda but not do the

work. The ones I know are incompetent and lazy.

program manager=somebody who has been exhausted

by their life in the product development trenches

and now wants a cosy administration role.

A colleague commented on reading this post that

it seems we can't get one good person anymore,

so we need a commitee to spread the blame!