I think msn is slower to react, ie. not as volatile as google so it might not be that easy to see changes quickly
I also think domain name means way more in msn compared to google
onpage seo more than google (which is all about strong backlinks)
in other words, if you are out to get number one for "porn" on msn and you are not porn.com, you might have an impossible task ahead of you
I also think that some things that might help on msn might actually hurt for google, so that is something to consider as well
