implementing spf

[Robert Storey]

I never heard of spf until yesterday, when there was a big discussion
about it on Slashdot. The discussion was very political (about
Microsoft, Richard Stallman, etc). I don't want to get into any of the
politics here, as it's not appropriate for this list. But I am
interested in the technology aspect. Specifically:

  1) Is the technology useful?

  2) How does one implement spf on the server side?

  3) How does one implement spf on the client side?

I most interested in No. 3 above - specifically, is there anything that
I must do as an end-user to make use of spf?

Thanks in advance,
Robert