I have tested both yahoo and msn and neither site junked any of my mail. It is true the MSN isn't setting up a SPF. I don't think yahoo will go a long way as long as SPF is enabled on there mail servers. Way too many corp. users' email get junked because of it.
edit: I re-read and I got it backwards. MSN was going to use SPF.. My appologies.
In other words, please ignore this post. It makes no sense.