I've been thinking over this for a while, and I'm still undecided. While 
some of the practical reasons SPF might be a pain in the ass for some 
people don't apply to me (most of my mail is run through servers I 
control and can use SMTP AUTH on, so the issue of sending mail from 
networks not 'allowed' to send mail for a given domain isn't an issue), 
there are other problems with its current implementation

http://homepages.tesco.net/~J.deBoynePollard/FGA/smtp-spf-is-harmful.html
Indeed there are problems with SPF.  SMTP is a very flexible and relaxed system.  SPF is not a "solution" it is merely a kludge.  A way for trying to stem the tied of SPAM to give us more time to find a real solution.  This kludge should be fairly good at helping defend against spam if it is adopted widely.  However JBP is much like many other nay sayers.  He provides many reasons not to adopt a system, gives you all the flaws in it but doesn't provide a decent practical alternative.  I think we all know SPF isn't perfect so his arguments add nothing new.

I did a little reading on IM2000 while I was at that site and it certainly sounds like it could be a much better solution in the long run.  However adopting such a system will require us to throw away IMAP, POP and SMTP and all of the software that has been written to work with those protocols.  It means re-wiring the Internet.  This isn't going to happen over night.  It will take 10 years (or more).  It will require the participation of a major ISP (eg AOL) and a major software vendor (Microsoft) to even get off the ground.  Certainly the free software world could potentially move a lot faster than that.  If there was an implementation of a free software IM2000 server and say a Mozilla.org client for it that would be a good start.  AOL has a fairly good relationship with Mozilla/Netscape and may be willing to listen.

Note that one of the main proponents of IM2000 is DJB (of qmail) fame.  AFAIK qmail has never been "Free Software".  In fact DJB seems to rather against OSS/FS.  He seems to be a bit of an egotist.  Which is why I've never had the desire to run qmail.

The May Linux Journal had an article on SPF as well, although I didn't 
read it well enough at the time to discuss. They were very much in 
favour of it, from what I remember.
That article was written by the guy who came up with SPF, the founder of pobox.com, a major mail-forwarding service.  Hence it was very pro SPF.

Regards
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