Have someone heard of the affiliate program network?

I have recently found out about the affiliate program network, and I was wondering if someone was acquainted with such systems.
I mean for business purposes (software selling).

Are these affiliate program network hard to set business?
Are they providing users with their affiliate program or do they involve the already set one?
Are they effective at all? Is there any sense to join them? If so, which one to choose:

  • Clickbank
  • BidVertiser
  • Copeac
  • AdToll
  • Shareasale
  • Forex-Affiliate?

Thanks in advance.