While I don't think anyone can give you an exact answer on that, it does seem that the most important thing is that whatever you do, keep it uniform.
In other words, if you are using "www.example.com/" to point to your homepage, then every single time that you point to your homepage in your website you should always use "www.example.com/"
The weird stuff and problems seem to come when people have links within their own websites that don't match, like having your navigation menu pointing to "www.example.com" but having other links within your own website pointing to "www.example.com/" or "www.example.com/index.htm"
Another great point brought up in an earlier thread (I can't find it, mabye someone else can) is that using the "www.example.com/" version (with the forward slash) is probably the best bet as it is the most direct path to the page.
But whatever you decide to do or use, ensuring it is used universially within your site is key.
The link into your site from other websites don't really matter as much in this sense as you aren't really supposed to be in charge of that or have control over how others link to your site.
Your concern is understandable but I would stick with the trailing end slash and keep things universal.
MSN results are often different than google results and as such, higher standings in one can mean lower standing in another.
It has been one of my most rewarding and frustrating experiences, but I have learned the benefit of "staying the course" in the end, it is better to decide once your structure, and then work work and work on building quality content. The rest will take care of itself. (After the whole painful waiting thing)
Best of luck!