Duplicate content is unavoidable....so I tend not to worry about it.
The search engines are smart enough to determine where "unique content" was first posted. So I suggest that whenever you write an article post it to your website and let the search engines index it there first.
You can monitor this via your server logs.
Then, post it to selected "established" article directories next, followed by distribution to other recipients using distribution hubs like isnare.com ---You need one way backlinks to rank well with Google and Yahoo.
I am not sure how MSN handles the backlinks issue but I believe it's along the same lines.
I think duplicate content becomes an issue when it's done blatantly like having the exact same content in two different domains or a sudden sharp spike in content which is already posted elsewhere.
A number of times when I "Google" an article that I wrote and posted to my directory first and then distributed later, I notice that Google search results bring up the article in well established websites/directories first, closely followed by mine.
I attribute this to the fact that these websites have "aged" over the years and Google attaches more "importance" to them --- this also does not worry me because my directory is less than nine months old as opposed to some of these websites which have been around for years and have "paid their dues" ....so to speak, and are high traffic websites.
Here is an good
article dealing with the importance of backlinks.
I find link exchange too tedious ....I still try to link to "relevant" websites reciprocally, but I am no longer as enthusiastic as I used to be a year ago. I prefer the "article method" for obtaining backlinks.